Oh, about the song swiping from "Tam Lin" ... that could no doubt be shown in some respects but is plenty false in others.
The English and Scottish ballads, for example, are full of borrowings ... there is enough originality in "Childe Rowland" to make it no less culpable on that score than, say, Laily Worm / Allison Gross and that family, or the various incest ballads such as Sheath and Knife, Leesome Brand, Lily Wan, etc. And all those are great favorites of mine, so I don't slander them in saying so.