Your explanation and usage of "New England" indicate that you incorrectly believe that name to have applied to the colonies in general, prior to Independence. Rather, that is only the name given to a small region comprised of a small number of colonies which, with an enduring continuity of identity, persists to this day. It wasn't a period term for America.
The fact remains that at any point prior to Independence slavery was the British Empire’s cargo, on board the Empire’s ships moving in between one of the Empire’s ports to another of the Empire’s ports. Nothing you can do to change that. That’s the factual timeline. America did not exist until Independence was declared. The date is July 2nd, 1776.
You were replying to:
"British warships were intercepting New England (especially Rhode Island) financed-built-owned-operated transports until well after the Thirteenth Amendment was ratified."
You can't very well blame the Brits for US domestic policy at that late date.
When you have something to discuss about early America and the colonies, let me know.