Nonsense, those British proclamations only offered freedom in exchange for army service, not general freedom for all African slaves.
And you well know why Lord Dunmore's tactic didn't work against George Washington -- because Washington out African-Americaned the Brits!
Washington did what Jefferson Davis & Co. never could: promised thousands freedom in exchange for service in the Continental Army, in integrated units!
And so many took Washington's offer that one British officer at Yorktown observed one in four of Washington's troops was black.
There were lots of black patriots in the Revolutionary war.