David of Manitoba has introduced some information on an apparent family of French Caldwell's who returned to Scotland.
I think that this is very important information and deserves starting a new "thread" on its own.
Firstly we should consider just what was going on in history on or about the relevant dates - I will get back into my books on this matter and report back.
For the purposes of starting this off I think the points to consider are:
1) the family seems to have been in France since before 1274 which is on the borderline on when Caldwell may have been a recognised surname.
2) the early versions of the name are spelled Calwel or Calvel - which might show a connection to Calw in Germany rather than Scotland. It only seems to become Caldwell when the family shows up in Scotland. This might just represent a "Frenchification" of the surname. David has already pointed out the French difficulty with "w". Even the Scots have difficulty in pronouncing "ld" and coupling this with a "w" close behind must be asking the impossible for a french speaker. Say "Caldwell" a few times and pay attention to what your lips (and jaws) are doing
3) Caldwell's were in Scotland before 1274 - are we looking for a branch that went to France and returned at a later date? Or are we looking at another source of Scottish Caldwell's? The wife of William b 1311 was Johanna. I am not a great expert of French first names however this sounds more Scots or English to me.
4) Find the places - Montherme is on the River Meuse in he Ardenne - it seems to be a village and is actually very close to the border of Belgium. Thge closest major town is Charleville-Mezieres. Cambrai is about half way between Montherme and Calais in the district of Nord and also close to the Belgian border. Le Cateau is very close to Cambrai. Abbeville is on the Somme near the coast and seems to be on the main road between Paris and Calais. After this "northern" connection Tartas is a bit of a surprise! It is on the River Midou itslf a tributary of the Adour which flows into the sea at Bayonne in the far South of France near the Spanish Border. What can I make of this? Bit early to tell - needs further research. However we know that the earliest recording with an English - sounding wife's name is in the southern part of Gascony thereafter the family moved to Northern France and stayed there for several generations before moving to Scotland. Much of France was an English possession in history terms and this will have to be checked with dates. There was also a wine trade between Scotland and Bordeaux.
4) Lord Jacques (John) is interesting and I have a Dutch friend by the surname Van Bladel - Bloedel might have been Dutch/Belgian/German? in extraction. Agneta sound like a version of Agnes (Dutch is Anja).
5) The Scots had strong connections with France through the "Auld Alliance" but the recorders of history seem to think that the French tending to think the Scots "rough, rude and uncivilised" whilst the Scots ended to think of the French (as the Australians succincly put it) as "up themselves".
6) Nevertheless many Scots were awarded possessions in France as reward for military service in the French cause (usually against the English).

These are not "findings" but the result of studying a simple general atlas and a few other musings. It is certainly a lead that should be exlpored more fully. Lets all start checking the internet!