In Cornwall we have some evidence of social repertoire from about 1620. Notwithstanding the remoteness of the Duchy it's clear that both instrumental music and songs from very far afield were known in Cornwall early on.

Evidence starts with London School viol music in the early 17th cent, and the Ballad of Chevy Chase was certainly known in Cornwall by 1690. I can quote many other examples. But we also have local English and Cornish language lyrics dating from about 1695 (Gwavas MS) and local tunes from about 1730 (John Giddy MS).

I suspect that the mobility of music means than in any region repertoire will be a mixed bag of local and further afield. However, the decision to call a tune, an element of style, or a distinctive repertoire 'Cornish', 'Hampshire' etc. is very much context driven- I can give you many criteria used when awarding such adjectives. Often such criteria require caveats concerning date, performance environment etc.

Processes in repertoire: I've identified 5 with a bonus. They are Retain, Create, Adopt, Modify, Discard. The bonus (a phenomenon of the last century and a half) is Revival. (Dissertation available on request!)

My vote is that the decision to study music considered 'English' must embrace relevant informing and comparative cultures. The way individuals and communities 'claim' music is probably worth a PhD on its own!