I'm no expert in this area by a long way but, presumably, after the collection and publication process had taken place by Sharp and others, there would have been, for some time, two parallel strands: (a) the continuum of the original singers in their locale - the Coppers being one example of this - and (b) the "tarted-up", arranged versions being introduced into schools and elsewhere.

Perhaps the effect of Sharp et al was to obscure (a) while bringing (b) into prominence - rather than remove (a) altogether.