I have wondered that if people compose new tunes to trad. songs (Rusby and N. Kerr quickly spring to mind), should they lose the right to the tune? My reason for wondering this is that if people pick up on what they hear rather going to source material, the altered material could become commonplace and considered traditional rather than attributed. I appreciate that part of the evolving tradition was that people altered words, tunes etc either in error or by design, but they didn't prosper from it. And what about tunes in sessions? A contemporary tune gets played and copied and turns up elsewhere, the author or source being lost on the way.