Jack's citation of lowland and continental repertoire in the Skene and other such sources puts me in mind of observations made in a major historical study of this period in Scotland which has just come out, reinforcing this cultural diversity:

The Literary Culture of Early Modern Scotland - Manuscript Production and Transmission, 1560–1625, Sebastiaan Verweij
Oxford University Press 2016, ISBN 9780198757290

Blurb sez:

This wide ranging survey of Lowland Scottish literary manuscripts devotes a complete chapter (number 7) to the background to Margaret Robertson of the Lude family and the compilation of her collection of verse. Since at that period such material would have been sung, probably accompanied by one of the family's harps, it is of interest, as its author states as an example that "both Highland and Anglo–Scottish Lowland musical traditions peacefully coexisted at Lude".

(Scroll down to near the bottom of the web page):
http://www.wirestrungharp.com/library/bibliography.html