Sorry - missed a bit:
"Apart from the fact that nearly all of these singers had a sizable repertoire of music hall songs and parlour songs all of commercial origin from the towns."
Totally irrelevant to the discussion - we are folk song collectors and enthusiasts, not oral or social historians or ethnomusicologists,
A traditional singer having such pieces in their repertoire doesn't make them 'folk' or 'traditional' any more than Dame Kiri Tikanawa singing 'Wouldn't it be Loverly' makes it opera.
It was our experience that singers - particularly those with sizeable repertoires compartmentalised their songs just a much as we do (or should do).
Walter Pardon called his folk songs 'folk songs', Mary Delaney called them 'My daddie's songs' even though she learned no more than a dozen out of a repertoire of around 200 from him. She refused to sing us her 100 or so C&W songs and told us she only sang them "because that's what the lads ask for down in the pub"; and "the new songs have the old ones destroyed".
It seems that it's only us (some of us) folkies who, for some strange reason, can't tell the difference between Max Miller and Harry Cox.
Jim Carroll