Folksong collectors,in general, collect only what they're looking for. In many cases, that brings a peculiar bias to the collection. I really prefer the "collect 'em all and let God sort them out" exemplified by Randolph and Hunter.
   I clearly agree about the worth of "The Mary Lomax Ballad Book" ( I should, I published it.) It presents a vivid picture of a traditional singer and her family, self-penned pieces, songs learned originally (by her father) from recordings and all.
   I strongly suspect that the idea of the illiterate singer, learning songs solely aurally, is a rarity, if not an outright myth.