The 1810 Buckingham Co., VA census shows Josiah Davidson with a son who could have been born in the 1790s. The 1850 Limestone Co., AL census shows the widow of a younger Josiah Davidson named Elizabeth (Hardiman) Davidson (and she was from Buckingham Co., VA). Living next to the Widow Elizabeth (Hardiman) Davidson in AL in 1850 was Martha Jane (Davidson) Gilbert and her husband Mace H. Gilbert (age 37; a teacher who was from VA). The Gilberts had several young children in AL in 1850, including a son named Thomas H. Gilbert and a daughter named Emily R. Gilbert.
On the 1870 Appomattox Co., VA census, there was a Humphrey A. Gilbert, and he had a son (age 5 in 1870) who was also named Mace H. Gilbert!
Note: There was an earlier Humphrey Gilbert in Amherst Co., VA, among many other Gilberts out there.
Back on 22 Nov 1831, Edward Davidson had married an Emily Gilbert in Amherst Co., VA. This Edward Davidson was apparently the son of the older Edward Davidson and his wife Judith Pendleton of Buckingham Co., VA. That older Edward Davidson (died 1827 in Buckingham Co., VA) was an older brother of the older Josiah Davidson (both were sons of the David Davidson (b. circa 1715; died by 1798) of Goochland/Albemarle/Buckingham).
The 1870 Appomattox Co., VA census mentioned above also shows that a Judith Davidson, age 76, was keeping house for Humphrey A. Gilbert and his family. This would have been the Judith Davidson who was a daughter of Edward and Judith (Pendleton) Davidson.
Humphrey A. Gilbert was married to a Judith H. Unknown. The 1850 Appomattox Co., VA census showed a 30 year-old Judith Davidson living with the older Josiah Davidson (the older of the two Josiah Davidsons was 83 in 1850). That Judith Davidson did not appear on the 1860 Appomattox Co., VA census. I wonder if the younger Judith Davidson was the wife of Humphrey A. Gilbert?
Based on the above, it certainly looks like the Josiah Davidson who moved to Limestone Co., AL was from the "Buckingham/Appomattox Co., VA Davidsons," and he was probably a son of the older Josiah Davidson who was 83 in 1850. Does anyone know the parents of the Emily Gilbert who married Edward Davidson in Amherst Co., VA, the parents of the Mace H. Gilbert who moved to AL or the parents of the Humphrey A. Gilbert who was on the 1870 Appomattox Co., VA census?