Thanks for the quick response. I've been reviewing the Southside Virginia CD by John Pritchett that was recommended by Dick Eastman and Pritchett includes lots of records on Henry or Henrie Briggs (in VA by 1657/58) and his descendants in the more than 4,000 pages of records. If I'm interpreting his records correctly, the Frederick Briggs (Robert, Samuel, Henry) who was born in 1745, married his first cousin Mary Goodrich in 1772 and died in 1789 after being found guilty of stealing horses. He wrote a long letter from prison naming his seven children as Nancy Goodrich Briggs, Howell, Edward, Clarimon, Thomas and Mary (Polly). All were presumably minors born during the 17 years Frederick was married to Mary Goodrich Briggs. I'm trying to learn more about what happened to the children to see if they settled in Buncombe, Yancey and Burke Counties, NC. This Frederick would have been 4th generation from Henry.
There is another Frederick Briggs on the CD that is 5th generation from Henry who was married to Mary Cooke. He is Frederick (Henry, William, Samuel, Henry). There aren't a lot of dates but Frederick's father Henry was b. 1737 - d. 1782, and Frederick was the 4th named child so one would estimate this Frederick to have been born perhaps between 1770 and before 1782. There is no mention of this Frederick going to SC but who knows.
If there are other Frederick Briggs of this period I haven't found them yet. I'm planning to go to the VA state library in Richmond tomorrow ans will let you know if I find anything more.