Thanks "M" for your comments:

Your examples and definitions of FPOC made me think of other examples that go beyond skin color.

I've read from Bennie MCRae's site that many gained freedom during the various wars in North America. The British for one offered freedom to Blacks if they fought on their side. I know that there are more, but I will have to "retreat" to Bennie's "Lest We Forget" page to other examples. This would probably account for such large numbers of Blacks who were free for more than 2 generations on the eve of the Civil War.

You mention that many Blacks came to the US
as free. Where could I find that information?

Your comments were extremely informative.