Of the 25 "by" I found in 1820, 11 were listed using the surname in 1830. There are no "by" names in the 1830 census, or in any of the other Accomac censuses. 1820 seems to be unique. In fact I've never see it before. Which is why it had me a bit stumped.

Other interesting thing is that in 1820 Acc there are 5 or more free persons of the same surname as those with "by" in the name. So, is it possible that those with "by" were themselves freed, and those without it were free at birth?

Will have to check out deeds and wills, but that obviously will take quite a bit of work. So may be a while before I get back to you with a response on those data.

By the way, I'm from Wash. Co. and have spent many hours in their records.