Jack,
What you say about Scott and Hogg (and others) is very true but at least Scott came clean and at least in the case of all the other collectors their manuscripts exist and can be compared. Buchan went way over the top (IMHO) and no field note type manuscripts survive or are ever known to have existed. The manuscripts at Harvard and the BL are actually copy for publication. The Harvard manuscript is verbatim the 2 vol Ancient Ballads of the North, with a few crossings out by the editors. There is a great deal of consistency in the 'adaptations'/'additions' he makes to his 'versions' which suggests largely the work of one man. Blaming Jamie Rankin for this is not on either. Bell Robertson knew Jamie Rankin personally and she stated he didn't have the wit to compose songs or doctor them to the level Child claimed. Nicol no doubt has to take some of the blame but not the lion's share.