Requesting Help With a Difficult Research

I am researching for information to write an article telling the true story of Sarah and Greene, her son. They were slaves of my 3d great grandparents, John and Elizabeth Hales, initially located in Oglethorpe County, Georgia. I suspect Sarah was born ca 1795 and Greene was born ca 1831. They moved to Clarke County, Georgia 1820, then to Walton County, Mountain District, Georgia from 1830-1850. I am sure they next moved to Jackson County, Georgia in 1850. If anyone knows what research step I need to take next in Jackson County, please share your ideas and suggestions. I have searched through the slave schedules in Jackson and Walton Counties without success. There are no matches for Sarah or Greene in the 1870 census records in Jackson or Walton. Finding them in an 1870 census would be a major discovery, but I do not see much hope in doing so.

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