Who told the stories at the time?
It seems clear from travellers writing about their tours in Wales in the 18th Centrury that there was a general understanding by the people they were writing for, and some of those would have been in Wales knew about the Atlantic slave trade and its implications.
Thomas Pennant
Arthur Aiken
Walter Davis, in "General View of the Agriculture and Domestic Economy of North Wales", (London, 1810)
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Authur Young
documents/silo.tips_arthur-young-agriculturalist-and-traveller-some-biographical-sources-1.pdf