Mel,

I have found this to be true immediately after reconstruction. I have a family of Glovers in Twiggs County, GA. The Glovers were one of the large slaveholders in the county and after 1870, most of the Glovers were black, and they carried the same Surname. There were several John's, Tom's, Mark's, etc... all unrelated. Their children were given the same names. Some moved to the adjoining county Bibb (Macon) GA where there were more Glovers.

Your case may be easier since thery were few black families with the same surname.

Follow your gut and keep digging.