"It poses many questions in particular the role of the singer in creating the song"
Plenty of evidence that they did create songs
Dig out the BBC recording of the Hebridean singers creating a song on the spot in praise of Alan Lomax's sexual attributes
We have a description of four men standing at the crossroads of the next village from here, tossing verses at each other until they's made a seven verse song
Another of a group of young, non-literate Travellers sitting on a grassy bank outside a church making a long song about how the wedding that was taking place would turn out

penultimate verse
"Oh the first year were were married was lovely
And the second we couldn't agree
An the third one she put on the trousers
And then made a wreck out of me"

That's why it is nonsense to suggest that singers had to rely on print for their songs
Jim Carroll