"NO NO NO NO NO,"
YES, YES, YES, YES.
Folk song research - in any form - is not (just) about collecting orally transmitted songs - it is about understanding our song tradition. In order to do this you have to take into consideration the singers' approach to songs that are not necessarily part of the oral tradition; (music-hall, Victorian parlour ballads, pop-songs of a given era......) they are all part of the singer's experience, therefore are part of our understanding of the tradition. No collector worth his/her salt would ever refuse a song from a traditional singer because it doesn't fit into their definition of 'folk'.
The question of the place of literacy in the oral tradition is very much in need of discussion - it is an extremely complex subject, too often approached on a far too simplistic level.
Has 'Fiddler's Green' been "orally processed" - how many significantly differing variants of it do you know? In my experience, it hasn't moved very far from its original conception.
Why didn't Sharp collect industrial songs - a whole bunch of reasons, nothing to do with personal taste. For a start, he chose to work in rural areas because he believed these to be the richest sources of what he was looking for.
There is no reason to believe that he was even aware of their existence.
Our knowledge of the urban repertoire, such as it is, is largely down to the work of MacColl (Shuttle and Cage/Second Shift, The Big Hewer...) and Lloyd (The Industrial Muse/Come All You Bold Miners... et al).
Self composed songs by traditional singers, and non-folk material in their repertoire is more about understanding the singer and his/her place in the culture rather than the repertoire itself. Revival singers play no more part in this particular body of research than do - say: Delius (Unto Brigg Fair), Vaughan Williams (Tallis/Greensleeves) or Butterworth (Banks of Green Willow) do - they were, as we are, borrowers/users/sometimes abusers of the tradition rather than participants in it - as I have said, a subject worthy of study in itself, but not part of our knowledge of the tradition.
Our understanding of our tradition must be based on our traditional singers - god knows, we're swimming in muddy enough water as it is, thanks to the revival largekly having divorced itself from its source music, without fouling up the picture even further!
Jim Carroll