Somebody has a lot of explaining to do.

Certified European historian Rozanne E. Folk (M.A., history) obtained a copy of the Registrum Monesterii de Passelat (Paisley Monastery). The first words in the Registrum referring to Caldwell are “Terra de Caldwell.” She found no mention of any individual with the surname Caldwell. Is there any possibility that she overlooked some reference in an entry of 1292 referring to a Caldwell, which the late Lesley Gordon claimed was present?

I understand that the term “de” commonly precedes a place name, rather than a surname.
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How far have we moved to a consensus favoring a reasonable probability that the entry referring to the land was made after the time when Robert Bruce, then Earl of Carrick and Baron of Renfrew, became anointed in 1306 by the Glasgow bishop as the King of the Scots (“Dei gratia Rex Scotorum”) and before the execution in 1307 of Reginaldo Crauford, mentioned in the entry, then Sheriff of Ayrshire? Reginaldo Crauford was slain in the expurgation of Templars in 1307. The entry refers to each such individual.
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Late 1307 was also the time that King Edward I invaded Scotland and Robert Bruce went into hiding. This might have been the year when the knight Caldwell died who left no male heir, but only his wife and daughter. After the mother’s death, his Estate may have passed to the daughter, whose status, wealth, piety, and perhaps romance resulted in a marriage proposal from Gilchrist Mure. Such a death would explain the absence of any Caldwell surname in the Arbroath Declaration of 1320. If the heiress were born in 1307, she would have been about age 26 when she married in 1333.
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Scot historian George Robertson claimed that the lands in question of the Caldwell heiress were located within the “Paroch Church of Neilstoun,” the patronage of which was given by Robert Croc, “Pro salute animae suae,” to the Monks of “Pasly” (Paisley), in the reign of Scottish King William [1165-1214]. (George Robertson, "A General Description of the Shire of Renfrew, including an Account of the Noble and Ancient Families, who, from the earliest times, have had property in that County, and the most remarkable facts in the lives of distinguished individuals. To which is added, a genealogical history of the Royal House of Stewart, and the several and illustrious families of that name, from the year 1034, to the year 1710; collected from public records, chartularies of monasteries, and the best historians and private mss. Published in 1710 by George Crawfurd, author of the Peerage of Scotland, &c, &c. and continued to the present period, by George Robertson, author of The Agricultural Survey of Mid Lothian, &c.” (hereinafter, History of the Shire of Renfrew, (1818), p. 41).
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“Paroch” is a term referring to lands administered by a Catholic church prelate (such as an abbot or bishop) or presbyter (church council).
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But Robertson referred to more than one Caldwell Estate. There were at least three Caldwell estates to the west of Loch Libo. If the Caldwell heiress’s “Terra de Caldwell” was entirely to the east of Loch Libo, it was not in the location where Caldwell Tower presently stands, to the west and north of Loch Libo. Robertson used a drawing by Timothy Pont of the 16th century that shows all of the Caldwell tower castles to the west of Loch Libo. This map can be viewed on line at National Library of Scotland. The castles would be part of what Robertson described as western Caldwell.
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The vast majority of tower castles in Scotland were erected in what Barbara Tuchman describes as the “calamitous” 14th century.
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Scot historian G.W.S. Barrow, in The Kingdom of the Scots (1973), states that all lands west of Loch Libo were part of the Ferenze Forest and kept as part of the demense of Walter Fitz Alan, who conveyed to Robert Croc only the lands of Neilston Parish to the east of Loch Libo.

It is unclear whether the reference to the Terra de Caldwell included lands both to the east and west, north and south of Loch Libo. The present day Caldwell Tower lies to the north of Loch Libo. It is not truly a 14th century tower castle but erected in the late 17th century from stones taken from the prior castle that had been dismantled.
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The lands of Renfrew are the first-mentioned of the estates specified in the charter granted by King Malcolm IV in 1157, in favor of Walter, the founder of that family, whereby he confirmed a grant which had been made by King David, who reigned from 1124 to 1153. The office of high steward of Scotland was also conferred on Walter and his successors, who from thence took the surname of Stewart, often, but incorrectly, spelt Stuart. http://www.pressinfo.co.uk/renfrew/town.htm.
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I have expressed surprise at the Caldwell spelling emerging at the beginning of the 14th century. The name of the Scottish Caldwell Estates have undergone a variety of spellings. A 1654 map uses the spelling Coldwel. (George Crawfurd and George Robertson, “A History of the Shire of Renfrew,” supra, p. 241.) In George Crawfurd and George Robertson’s History of the Shire of Renfrew, supra, Caldwel is the spelling most often used. In early correspondence to William Mure in the first quarter of the 18th century, Sir David Hume, famed Scottish philosopher, addressed his letters to William Mure at Calwell. Later letters used the Caldwell spelling. A January 11, 1760 pleading before the Scottish Lords of Session lists counsel as William Mure (1716-1776) of Caldwall. (Answers for William Mure of Caldwall, Esq.; to the petition and complaint of Daniel Campbell ... William Grahame ... and Alexander Cunnynghame, ..., National Library of Scotland, microfiche). Throughout the nineteenth century, the Caldwell spelling was used by a later William Mure of Caldwell, author of numerous books. (See online catalogue, National Library of Scotland.)
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But there is yet another source indicating the spelling of Caldwell in the 14th century. According to Samuel Cowan, author of "The Lord Chancellors of Scotland," W. & A.K. Johnston Limited, 1911, vol.1, at p. 163, William Caldwell was appointed Chancellor in 1349 and served until 1354, when he died. Cowan reports that William Caldwell presided over Parliament held at Dundee, where the Estates discussed the ransom of King David, who had been imprisoned for 11 years. Lord Chancellor Caldwell pleaded for payment of the ransom, but the nobles allied themselves with France, and invaded Berwick, then held by the English. The Scots, led by Baliol, were defeated. When Caldwell's successor stepped in as Chancellor, the ransom was paid in 1354. Cowan writes that there are no documents describing the official duties of the Chancellor. He ranked below the High Steward but above the Chamberlain. The Lord Chancellor was responsible for administering the laws and presiding at courts of justice. p. 6. The position was usually given to the most learned and scholarly men of the time and most influential with the King. p. 11 Up to the Reformation, the Lord Chancellors were usually Catholic Prelates. p. 12. Many had university training in France or Italy. p. 6. In reading Cowan's book, I discovered that Sir Reginald More never was appointed Lord Chancellor. He served only as Chamberlain.
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From various web sites I learned that William Caldwell was a prebend of the Diocese of Glasgow that encompassed both Ayrshire and Renfrewshire. I was unable to find or recall a reference indicating he was the bishop or archbishop, although many of his predecessors were. If so, he would have held positions both as head of the ecclesiastic and secular courts of 14th century Scotland. He likely would have been among the wealthiest individuals in Scotland, yet no document has been revealed establishing what lands he owned or possessed. As prebend wanting to increase the tithes or rent payable to the Church, a Prebend likely would favor the clearance of forests so that land could be used for pasturage. The settlers who rented these cleared areas might have assumed Caldwell as their surname.
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Barrow lists in the Kingdom of the Scots (1973) the more important charters for lands Walter Fitz Alan granted to others. The list does not include reference to any Caldwell by surname or place name. Robert Croc is listed. How then do we explain William Caldwell being a prebend (trustee) of lands used to support the Glasgow Diocese?
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Did Walter Fitz Alan or his successors designate William Caldwell to serve as the prebend, such that upon his death, management of the lands passed to another prebend or to the Church, rather than into his personal estate? Such a theory can explain the absence of a charter by which the lands became part of his hereditary estate. The administrative burdens associated with being a prebend for the benefit of the Church may have necessitated a highly educated and devout individual.
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With so many dying during the Plague of 1349-1350, William Caldwell would have been in the position as chancellor to ensure that the people to whom he designated successors to those who died without heirs would bear the Caldwell surname. Another consideration is that the Paisley and Glasgow abbeys and cathedrals were mother churches that promoted daughter churches in the outlying areas throughout Renfrewshire and Ayrshire. If William Caldwell were an archbishop, he might have fostered adoption of the caldwell surname among the members of these daughter churches. Finally, it appears that the use of surnames became much more common following the Plague. All of the chancellors after William Caldwell bore surnames, while only 5 of 12 before him used surnames. These circumstances could have played a large role in widespread and rapid proliferation of the Caldwell surname at the end of the 14th century in Ayrshire and Renfrewshire.
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I previously wrote that Gilchrist Mure [aka Gilcrist Mure] acquired the majority of the Caldwell Estate in present day Uplawmoor, East Renfrewshire, Scotland in the 14th century. This was based upon two secondary sources: (1) "The Statistical Account of Ayrshire by Ministers of the Respective Parishes," published 1800s by William Blackwood & sons Edinburgh, states Gilchrist second son of Sir Reginald [Mure], acquired the Estate of Caldwell by marrying the Heiress of Caldwell of that Ilk." (See posting here, 3/6/02. David Caldwell, Manitoba) (2) Burke's Landed Gentry states Gilchrist More acquired the estate of Caldwell in Ayrshire and Renfrewshire through marriage with the heir of Caldwell, of that ilk. (http://www.burkes-peerage. net/sites/common/sitepages/page13b-may.asp, From Caldwell To Tasmania)
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Tom Caldwell and Barry Robertson have asserted that the Caldwell heiress married Godfrey Mure, not Gilchrist Mure
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Tom Caldwell wrote 1/17/02 that a female Caldwell descendent married Godfrey son of Gilchrist Mure of Cowdams who became Mure of Caldwell. On 2/28/02, he again stated the heiress Caldwell married (?circa 1350) Godfrey son of Gilchrist Mure of Cowdams. He mentioned however, that his source was uncertain.
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In his article, "The Caldwell Mystery," posted here on 2/23/02, Barry Robertson cited ‘The History of Neilston’ (1910) by Doctor David Pride, who wrote that the Caldwell Estate came to the Mures through the marriage, in 1347, of a Godfrey Mure to the heiress of Caldwell, she being of ‘That Ilk. Robertson also noted: "It seems that the Lady of Caldwell did not own all of the estate - a younger male branch of the family held Little or Wester Caldwell – the area surrounding the present Hall of Caldwell, including the area later to become the golf course. Little Caldwell did not come into the Mure possession until towards the end of the 17th century."
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David Caldwell of Manitoba informs us that John Mure of Caldwell is the first who was designated the first of the name who appears designated "of Caldwell," in 1409. In contrast, Barry Robertson had stated Godfrey became Laird of Caldwell in the right of his wife, taking the title due to its existence in the first place.
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William M. Metcalfe, D.D. (1840-1916), authored "History of the County of Renfrew, With a Map of the County," 1905, Paisley: Alexander Gardner. Copies can be found at the LDS Family History Library in Salt Lake City and at various universities (e.g., Cal Berkeley). It is now online at google/books. He wrote: "Godfrey Muir is the first who is designated of Caldwell." (p. 105) Possibly this is because he is the first of the Mures to be born on the former Caldwell Estate.
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Metcalfe states that the estates of Caldwell in the counties of Ayr and Renfrew were acquired “at the close of the fourteenth century” by a marriage with the heiress of Caldwell of that ilk, then a family of some note, having given a Chancellor to Scotland in 1349. (p. 105) Metcalfe cited as his sole source "The Selections from the Family Papers Preserved at Caldwell, 1696-1853," edited by William Mure. Glasgow: [printed by W. Eadie for Maitland Club]. no. 71 (part I).
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George Crawfurd (1710), History of the Shire of Renfrew, declares that the Caldwell Estate largely passed into control of the Mure family when a Caldwell heiress “of that ilk” married Gilchrist Mure in 1333.
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Metcalfe cited the Maitland Papers as the basis for stating that the heiress married Godfrey Mure in 1347.
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Which is more likely correct?
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Gilchrist Mure was born 1301 in Cowdans, Linlithgow, West Lothian, Scotland. He was the son of Robert Reginald Mure (1267 - 1329). He would have been about 32 if he married the Caldwell heiress in 1333. If she were age 24-26 when she married, her year of birth would be about 1307-1309. This is the time when King Edward I invaded Scotland, and Robert Bruce fled Scotland and went into hiding. Perhaps the struggle to protect him led to the demise of the heiress’s father.
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Gilchrist's first son, Godfrey Mure, was born in 1352, possibly in Linlithgow, West Lothian, Scotland. Clearly he could not have married the Caldwell heiress in 1347, and it seems unlikely his mother could have been the former Caldwell heiress.

I have read Metcalfe's book, available online at google.books, but not the Maitland Club Papers. Assuming that Metcalfe correctly paraphrased the information contained in the these Maitland papers, I have to conclude that the Maitland papers are in error in linking a 1347 marriage of the Caldwell heiress to Godfrey rather than Gilchrist. Godfrey had not yet been born. Gilcrist needed a male heir. At the time Gilchrist married the heiress of the Caldwell Estate, she likely was kin of William Caldwell, then Prebendary of Glasgow, and soon to be appointed in 1348 Lord High Chancellor of Scotland.