At all the clubs I went to you could expect to hear mostly traditional songs, if that is what you mean by "folk". You could also expect to hear other songs which fall within the wider meaning of "folk" - I know you deplore that usage and I sympathise, but it is now how the word is generally understood,and the clock cannot be turned back.

I don't think I've ever heard a Buddy Holly song performed seriously in a folk club, although I have once or twice heard one done tongue-in-cheek as an encore after a set of largely traditional songs.

I went to the Empress of Russia a couple of times when I briefly lived in London, and I distinctly recall Bob Davenport singing several songs which I would not regard as traditional. However that was around 1980 so perhaps it had 'deteriorated' by then.

There were certainly a few clubs known for having a "trad only" policy but they were regarded as something out of the ordinary. I don't think the term "folk police" had been invented then. I think you must have been fortunate to be able to attend clubs which had this, or something close, but except possibly at the very beginning of the folk club boom (which I didn't experience) I doubt they were typical. Through most of the boom period, which I regard as having continued through the 70s and 80s, I would say clubs of the sort I attended were more typical - predominantly British traditional song but with a variety of other stuff. That seems to be the experience of others too.

I strongly disagree with your claim that this broader interpretation of "folk" prevented me from hearing and performing traditional songs.