As for "knowing who wrote it," I have to agree with Lloyd's citation of a European collector (Bartok?) that, essentially, "a peasant pot is still a peasant pot even if we know the name of the potter."

Of course, if there are considerable and interesting variations, the name of the original potter/creator becomes moot, even if known.

On the other hand, the amount of verbal variation in most songs by known writers (say, "This Land is Your Land") is almost negligible.

That is especially true in societies like ours right now where people want to "do it just like the album" and love correcting you. Remember the other-thread controversy about whether Anais Mitchell sings "Carter Hall" or "Carterhaugh"? Really, why should anyone care?