> singers who had learned songs from bound books tended to sing them exactly as they had learned them, while those printed on "ballads" were treated as "changeable" at the whim of the singer - a sort of respect for the published word.

Sounds like the "book" singers may have been better educated (more books in their lives). Did "book" singers also learn many songs from broadsides? On the average, do we know about how many songs the "book" singers sang in contrast to the "sheet" singers?