>>>>>What if the 'new' version is absorbed into the tradition,and sung a couple of decades later, then collected again with still more alterations? <<<<<
I think I have come across probable examples of this. The simple answer is if they have gone back into the tradition then they are traditional but any researcher worth their salt would want to know about the mediation. Your Sharp example fits in with this. I can only answer personally, I have just read DaveH's thesis and he gives an example from Frank Hinchliffe's repertoire. I also have come across examples. Personally I record everything and present everything so it doesn't affect me. However, I must confess that having recorded as much of a singer's repertoire as possible I would personally value those songs that had more likely been much longer in tradition. I can't speak for others. What about you?