Here are some notes of mine on 'Sir Cawline' (Child 61):

Until recently, only three versions of this ballad were known. Child included all three in his 'English and Scottish Popular Ballads', with his main text, an English version called 'Sir Cawline', derived from Bishop Percy's 'Reliques of Ancient English Poetry' (1765). The other two versions, one collected from a Mrs Harris of Perthshire in 1859, and another reproduced from Peter Buchan's 'Ancient Ballads and Songs of the North of Scotland' (1828) were considered by Child to be corruptions of the Percy MS version.

However, in the early 1970's, Marion Stewart discovered a late-sixteenth century (c. 1583) Scots poem entitled 'Ane Taill of Sir Colling the Knyt' in a manuscript at Register House in Edinburgh. Her analysis demonstrates that both the Harris MS and Buchan MS versions are derived from a source shared with this 'Sir Colling', and not the Percy MS. Moreover, Child had dismissed the first two stazas of the Percy MS, mentioning Christ and Edward Bruce's campaign in Ireland, as belonging to another ballad. 'Sir Colling' shows that these stanzas are relevant to the setting of the story.

See:
'English and Scottish Popular Ballads' vol. 2 (F. J. Child, 1882-1898) pg. 56-63
'Scottish Studies' 16 (M. Stewart, 'A Recently Discovered Manuscript', 1972) pp. 23-35
'The History of Scottish Literature' (ed. R. D. S. Jack; Hamish Henderson 'The Ballad and Popular Tradition to 1600', 1986). Reproduced in 'Alias MacAlias' (Hamish Henderson ed. Alec Finlay, 1994, 2004) pp. 78-94