"Collectors were mostly pretty explicit about that they were doing, and you're deliberately misrepresenting a completely logical set of priorities."

I completely agree with Jack Campin here. Just imagine you've just met old Mrs X in Village Y. She's got 21 songs which are made up of 6 ballads, 14 lyrical pieces and a recent music hall song. You've got a notepad and pencil and a limited amount of time in Village Y. Are you going to spend any of that time noting down the music hall piece?
Of course you're not!

Fast forward 100 years and your descendant meets Mrs X's descendant in the same village. This time your descendant is armed with a state-of-the-art electronic recorder. Now your descendant might have the luxury of recording that music hall piece (or 1940s pop song)for the sake of completeness.