Just looking into the oral tradition among families will give some answers. MY father was a first generation American of Austrian immigrants. He was orphaned at age six and grew up on a farm in Central New York State before and during the depression. The songs he knew from the farm hands and the travelling harvest companies were the bulk of what he knew outside the popular songs o the radio.

I knew songs from movies like The Bold Fenian Men from Rio Grande. And Shenandoah from a TV series called The Long Gray Line. And I would sing them or at least the melodies long before I was aware of them as songs from any tradition.

I think there are songs that we just absorb out of thin air because we heard snatches of them in the back ground as we lived. And we assembled them into complete songs over the course of time.

Don