“I don’t see how half of them are Appalachian English. Words and phrases like “to let on,” “kindling,” “hull,” are just basic English, many of them older than the settlement of the Appalachian.”
I think that is precisely the point. The idiomatic language of the Scots Irish originated in Britain and was brought to America with the settlement of the Irish Protestants in the Appalachian area of the US. The words themselves are old English or as in the case of a word like “kindling” are of Nordic etymology. The isolation of mountain people allowed them to hang onto the original language much longer than the rest of the USA.
My point is: since when did the rest of the USA lose words like “hull,” “kindling,” etc.?