However, if I understand you correctly, are you saying that pre-20th century, Black people in the USA exerted a highly significant influence on that nation's culture, but prior to the 20th century emigration to the UK of Africans & Caribbean people, the cultural influence of Black people in the UK can't be documented?

You can't have an "influence" unless two groups are able to listen to each other.

So before immigration in the 1950s, black Caribbean music had no influence on UK folk, because there was no opportunity for people in the UK to hear it. But white US folk *did* have an influence on white UK folk, because there was substantial communication between the two groups - it didn't change the style of UK folk, but it did mean that some tunes like "Someone's in the kitchen with Dinah" got picked up by performers and would be known by the British audience. So before 1950 or so, the only black influence on British music would have been indirectly via American music, and then only in some bowdlerised version suitable for a white audience.

After 1950 of course, British music took off with the combination of British, Caribbean and American influences, and all those influences have vastly expanded what we play. But none of that is generally considered to be "traditional" - "traditional" in a British context would be taken to mean songs in the style of that country's historical inhabitants, which excludes "old-timey" and calypso.

Graham.