Dave Bryant,
what happened that evening with Dave and Peggy is indeed sad, infuriating even. However the incident proves that their "mark" had been made, even if their faces were not recognised.
Me, being nowhere near their ability/status, I actually have a dream of something like that happening to me: to walk into a club and hear a floorsinger doing one of my songs, not knowing it's mine. When-if that ever happens, it will mean that I have entered the "fabric" of folk music, even as a little thread.
But you don't easily recognise threads in a fabric, it's the whole that matters (unlike in pop music, where stardom and personal recognition/glory is what everyone strives for). In such a context there is (somewhat perverse) pride to be gained in anonymity.
Dave Webber has already been blessed with his Maysong and Parting songs being dubbed as "traditional", to the point where he had a really tough time claiming royalties for them. I'd rather have that than the transient glory of star billing or a few hundred pounds more per gig.
Though, fair is fair: To have both is better!