I promised myself I wouldn't get involved, but here we go anyway. The point I want to make (and it's a minor one) is that 'source singers' 'the wellspring' or whatever else you call it *was* quite exposed to outside influences. There are a whole load of irish songs and tunes that went to America and came back or were even written in America and came over to Ireland. Likewise, you'd find it hard to claim most maritime music was locked into the one region tribe etc... (you could suggest that it was more restricted to sailors, but sailors surely had loads of contact with landlubbers even back in the old days when voyages were longer.) Broadsheets were all over the place. A lot of movement between classes has also happened, (eg the links between various folk dances and court dances at one time or another.) Even recordings of folk are older than the fifties. I think it is slightly naive to see any period as being characterised as a time when music was definitely locked in to particular communities exclusively. I'm probably going to be told I misrepresented people's views and/or am simply an idiot but there we go.