Wow, the discussion has moved apace; sorry, I am out of contact with only intermittent internet access. LEJ, good description of the steps of the process; I tried to challenge it in my mind, but failed - it seems to fit all examples I can think of. Scrump, beyond a certain amount of change, the song could be deemed to have a new variant, which could be attributable to whoever made those changes. A little bit like parodies can be attributed to the latter writer, even though a nod is given toward the original. And the two variants can co-exist without a problem, I think.