All unknown territory I'm afraid Lighter.
It certainly wasn't a case of 'book singers' being better educated; on the contrary, the lesser literary skilled ones tended to be in awe of the published word.
Many singers learned the songs from ballad-sheets, but some of the bigger repertoire ones, (Tom Lenihan being an outstanding case) though he might have filled out part songs from them, always said that he didn't "trust them".
Again - no hard and fast rules.
Just a point - Walter Pardon, the last of the English 'big repertoire singers', made a point of writing down the songs his family songs - his main source being his uncle Billy, who was born in the 1860s I think.
Walter told us he never saw or heard of a broadside.
Harry Cox had a large collection of broadsides - Bob Thomson sorted them out for him before he left for America.
According to Bob, Harry was quite adamant that he never learned any of his songs from them - make of that what you will, but there was no reason for him to lie - it didn't matter to him one way or the other if people knew where he got his songs from.
Jim Carroll