Richard Vaughan and Sally Clark would only be listed by name in the 1820 census if they were "free" at the time the census was taken.

Beginning in 1793 VA began keeping a "Free Negro Registers" of the free blacks in their counties. It identified them by name, age, sex, colour, how and when freed either by Will or Deed or "born free of a free mother"...status of whether born free is based on the status of the mother.

Registers for Henrico County still survive at the LVA.

Free Negro Registers 1825-1858 50 items
Registers of Free Negroes and Mulattoes, 1831-65 4 volumes
Emacipations, see Court Records.

Beginning May 1, 1806 those freed after that date were to leave the state within 12 months......or petition the court to stay, or risk being re-enslaved.

It might be worth a try to look at them.

Selma