Can I add that, as far as I'm concerned, I'm happy to accept that there are marginal cases - Nick mentions Buttercup Joe, I would add the Irish song A Stor Mo Chroi
Both have known authors and neither have departed far from their original form, but nobody would argue that they haven't become firmly established in the traditional singers's repertoire
When it comes to the folk arts, there are no rule-books, bt as an active researcher I need to set some perimeters to my identifications
Jim