I don't know if that is specifically true about Aunt Molly Jackson and Lomax, though it would not surprise me. I believe it is true that various settlement schools bought Child Ballad books because they were considered appropriate materials for appalachian boys and girls. So when collectors showed up, they might get songs sung in someone's family filled out with verses learned from the books.

As for Ewan MacColl, I also don't know that he ever tried to pass a reworked song as a product of the tradition. Brian was just wondering...