Hi Nick
Not sure if you're referring to the book title or just the concept in your final sentence. Personally as you would expect from my previous comments it matters a great deal to researchers into the history of individual songs. My own thought on the examples that you give is that any mediation by source/vernacular singers is simply part of the vernacular tradition, call it what you will.

However, sophisticated editors mediating material and then trying to pass it off as directly from tradition, is not just deception (whichever way you look at it) but causes a great deal of misinformation in research.

Whether there is a grey area between the two is something I have not yet looked into.