As far back as 1971 there was an indication of what was happening to folk music, when Bob Pegg let the rat out of the bag at the National Folk Festival at Loughborough.
To a questioner who asked what motivated him (35 years ago) he replied,
"I'm no longer interested in folk music - I'm in it for the money".
I still treasure Trevor Fisher's thoughtful pamphlet in response entitled 'We're Only In It For The Money'.
Richard; sorry to persist with this, but I find I am now banging my head on the limits of my understanding of copyright (not really my interest, but how creativity among traditional singers is estimated does interest me).
How many of the features you listed above have to come into play before it can be considered that a singer has re-worked a song enough for it to be regarded that it is a product of his/her creation.
Each time John Reilly sang 'Well Below The Valley' the verse structure altered radically, the tune varied likewise, the only thing that remained constant (more or less) was the text. How does this differ with what Phil Coulter did to it in order to copyright his arrangement?
We recorded Walter Pardon and Tom Lenihan talking about altering songs to suit themselves, and in Walter's case, have before/after examples.
Don't wish to be a pain in the bum (not at the moment anyway)
Jim Carroll