Hail Rirchard - saver of BBs ankles.
The International Folk Music Council definition was flawed from the outset: it is debatable that there has been 'a community uninfluenced by popular and art music' in England for several Centuries. However, the critical part of the definition (the 3 'factors' in para 1, together with the 're-fashioning and re-creating'in para 3) focus the definition on the performer, rather than the content, and define him/her as creator rather than copyist. And for that we have to thank Douglas Kennedy.
How come Brian Peters nearly always makes such sense? However, Brian's definition of traditional singer makes Barbara & me traditional singers - which lots of people wouldn't like to contemplate - we'll leave that to other's judgement!
On another point, I can't think of a single 'traditional singer' (as defined by general concensus - who's consensus? err...) who hasn't added to their repertoire from contemporary sources (be it broadsides or some singer/songwriter who's LP they have). Given that, then CONTEXT OF PERFORMANCE becomes, again, a critical factor in defining folk music.
Once again - in response to Cristian's initial posting - make sure you've got your definition watertight for the purposes of your thesis. Everybody elses definition than become irrelevant to the work you are doing.