Steve.
In the ballad of Barbara Allan, Ayrshire version, do you or others not find traces of an older ballad? I have pointed out local features in previous posts which would fit a version for this area

Captain Carr, it must be now accepted, is localized for the same area and if a 14th.C. date can be established for the burning of Lady Loudon and her nine children this would pre-date the burning of the house of Towie in 1571 by Edom o Gordon or Captain Carr
This does not of course mean that the Ayrshire ballad was composed before Edom o Gordon but having the name Captain Carr included in the latter must surely give the ballad experts food for thought.

Lambkin--when did the name die out in the Loudon area, it certainly would not have died out with the principle land owner when the lands passed to an heiress if other families are any guide.
The first castle of Loudon, so called, given the status of the owners, would be considered the prime castle in the area.

On the whole I would say that Lambkin would be the least likely of the three to give the experts cause to revisit it to pin down a locale.