The problem with this type of discussion is that all the sources seem to contradict each other. For example:
"The Negroes in the American continent, for instance, speak various languages according to the particular area they inhabit. Most of them speak English; in Brazil they speak Portuguese; in the rest of South America, in Central America and in parts of the United States, they speak Spanish; and in certain areas of the United States and Canada they speak French. "On Cape Breton island in Canada, there are even Negroes who speak Gaelic" (Julian Huxley, We Europeans, 1936 p. 123)."
At some stage I think we have to look at the music itself and consider the 'gut reaction' of musicians who play the stuff, and then look at the "sources".
I'm increasingly convinced the historians only ever see half of half the picture, if that. It why I think the Oral Tradition is so important.
While this side of the Atlantic we have a pretty good concept of what we undersatnd by the Oral Tradition. Because of the history of the States over the last three hundred years that picture is perhaps less clear because of the vast range of competing cultural influences. Whatever else, it gives amazing vitality and drive to the music.
Personally, I would rather hope that an Amercan Oral Tradition would embrace and acknowledge all these influences.