"A performer could write a ballad in a traditional mode, invent a provenance and the vast majority of the audience wouldn't know it wasn't original."

That brings to mind the stories (which I believe to be true) about Ewan McColls songs written for the Radio Ballads in the 60's. Apparently several of the songs (eg Shoals of Herring) were claimed by some old folk to have always been in their repertoire, having learned them at an early age. Yet they had only recently been written. The songs must really have struck a chord with these people. Not quite sure what McColl thought but I think he was quietly pleased about it.

Ged