or that all music is traditional music, or that all music except folk is traditional music,

To quote Howard again: That seems to be how traditional singers treated songs, with both tune and words likely to vary from one repetition to the next. It's something which revival singers mostly appear to have lost.

To what extent can we say Folk is a Traditional Music when it is, in effect, a construct based on a concept of a traditional music operating a very significant and cultural, historical & social remove from that which was the actual context of the music in its traditional state? Of course we might discuss the conventions and affectations of The Revival as being a tradition in themselves, but that is, perhaps, a very different thing to how most folkies would think of the music they do as being traditional.