Surely "tradition bearer"and "song carrier" and such terms are completely different from "source singer". The former two terms are generally used to refer to revivalists who have a particular respect for traditional ways, and make a point of learning from "source singers" and passing the stuff on. "Source singers" are the real deal, however you care to interpret that. "Source singers" are Harry Cox and Leadbelly and so on(But beware: Leadbelly, and Fred Jordan, learned songs from collectors as well!). Other terms are used for Peter Pears, Martin Carthy and so on, those who love traditional songs and have reinterpreted them. Martin Carthy showed greater respect for traditional ways, Peter Pears showed little or none, in his performance that is(I've no idea what he listened to in private).
   Tunes are quite different, in England at least, in that the "tradition" lasted long enough enough(in the dance bands) to overlap and interbreed with the "revival". Ot at least, that happened in the north. I can't really speak for what happened in the south.