Don't know if it helps, but I have a lovely memory of the traveller singer and storyteller Betsy Whyte at a performance in Kilmarnock folk club in the early 80s (?).
At around 9.45pm she started off on a story of the Silly Jack variety -- set him off on his quest with many variables and lots of repetitions, and 45 minutes later the organiser was subtly indicating a wind-up sign. A true professional, Betsy brought the story to a conclusion in a most tidy and satisfactory way, so that everyone felt they had resolution -- but my car passenger on the journey home told me that she had embarked on a major tale and was, in fact, only a third of the way through it!

SO, should we rather be applauding the creative energies of earlier performers who might have annexed other stories for their own purposes, rather than seeking for a possible UR-source which may never have existed?

I realise that there are potential confusions in my argument, but I'm pushing for the position that singers make 'good' versions to suit their own (psychological) reading of a basic text. And I'm also willing to bet that sometimes they may not even have realised that they've done so!