I was talking there about song collecting. Instrumental music is interesting in its own right, but the OP was asking about songs. There is source material pre-1880s, just not enough as far as I know now to make meaningful comparisons, e.g. between singers of several generations in the same family or village.

You could also argue that song collecting went on post 1920 as well, but the picture then gets complicated by records, radio and so forth.