Jim -
Sorry Vic - you (and everybody here) is ignoring the uniqueness of fok songs and ignoring Bert's closing question - what are we going to call this bunch of unique songs - or maybe they are not unique
Would you like to be the first to say they are not?

It would be helpful, then, to identify what Bert's closing question was - and the context he said it in.
Are you talking about the end of his Folk Song In England? He does not seem to be asking anything about the uniqueness of folk song there. To my mind the most telling sentence in that last paragraph is -

Rather than say 'the folk is dead' and attempt to keep folk song alive as something quaint, antique and precious, let us say, 'the folk is changing' - and song with it and then help what it is changing into.

I can go along with that concept of changing. One interpretation of it could be that this statement is anticipating the approach shown in Steve Roud's book.