Print and person adaptation has always been a feature of song transmission as far as we know - Anna Brown and all those cited by David Buchan in 'Ballad and the Folk' are worth bearing in mind in this respect.
Duncan Williamson had an extremely fine repertoire of traditional ballads - inauthentic?
Many of the singers we recorded supplemented their songs from printed garlands and ballad sheets Tom Lenihan and Martin Reidy in particular (see Clare County Library collection above)
Walter Pardon gathered together his 2 uncles' songs and, where they were incomplete, filled them in from wherever he could get them.
The problem is in all this that we have no idea of how the oral tradition worked as the songs were treated as artifacts and the singers were never asked their opinions - this, I believe, has left the field open for all sorts of unsubstantiated speculation. to be presented as fact when there are no grounds for doing so.
In our experience, the oral/print question is an extremely complex one.
That 'the folk' were capable of creating good songs themselves has become beyond doubt since we began our work with Travellers and here in West Clare - in the case of the latter, we have found dozens withing a ten mile radius of this fairly remote one-street town and have been told of many more which have disappeared.
As for the quality of a song being an indication of validity - I suggest that you seek out Roscommon Traveller, Martin McDonagh's exquisite version of 'Lady Margaret' (Young Hunting) or Mary Baylon of Louth's 'Johnny Scot' or the County Dublin version of Prince Robert ('Lord Abore').
Jim Carroll