I dunno about Scott's authorship, of the "Corbies," Steve. According to Malcolm Douglas on

https://mudcat.org/thread.cfm?threadid=9564&messages=47#1238100

"Scott ...was sent it by Charles Kirkpatrick Sharpe, 'as written down, from tradition, by a lady' (Minstrelsy, edition of 1812: II, 214). Child (I, 253) quotes a letter from Sharpe to Scott (August 8, 1802): 'The song of 'The Twa Corbies' was given to me by Miss Erskine of Alva (now Mrs Kerr), who, I think, said that she had written it down from the recitation of an old woman at Alva."

Which is not to say that it was old at the time.