"I assume from your last line that it does include "pop songs, music hall songs, stage songs.." that have "been subjected to the folk process.""
That goes without saying Dave - ad children's adaptations of modern pop songs and tele adverts
What happens in folk clubs is irrelevant though - change for change's sake is as irrelevant as simple repetition and folk clubs don't count as communities any more than do concert halls that put on adaptations of folk songs by Vaughan Williams, George Butterworth or Percy Grainger
Now if a bunch of kids got hold of Bue Moon.... different kettle of dingbats
One of the fature of songs in print or performed on stage is that they tend not to change or be adapted - they tend to remain as first heard.
Print had the same effect - we spoke at length to singers who had learned from ballad sheets (the later form of broadside) who told us that they regarded the version in print as the right one and unalterable
On e other hand, they had no problem with filling out songs they already knew with verses from print
I's not really complicated, just a bit detailed, but once ou get the hang of it it makes sense and it really is agreat fun sorting out one from the other
Jim