I remember reading a book, I think it was David Buchan's "The Ballad People" over 30 years ago, where he studied various versions of traditional ballads and came to the conclusion that at that time in Scotland, songs were remembered by use of a narrative skeleton into which "floating" verses could be slotted, so that apparently different versions in the collections of that time were in fact what would have considered the same song by the sources.

That is my main objection to printed sources, in that they remove the ability to vary the performance according to circumstances.

In modern times, I don't think Dylan has ever had definitive versions of his songs - just compare the "Freewheelin'" and Hallowe'en '64 versions of "Don't Think Twice".