Mark, thank you for continuing our efforts to learn more about the Floyd families of Horry County.I know they are all related somehow.
Secondary evidence does seem to indicate that Frederick Floyd (b.~1769) was married twice.I believe that Frederick died before the census of 1820 was taken and that the Sarah Floyd, Widow, listed on p7 of the Horry County SC census is his widow.There is also a James Floyd son of Frederick listed. Everyone needs to read the actual census of 1820 as some of the printed census books are wrong.
As for the children that you list: 1) Katherine (or Catherine) may have been born ca 1795-1800 per some of my research.
2) Samuel Floyd (b.~1791) moved to Simpson Co MS and raised a large family.This is my ancestor.
3) James Floyd (b.1790-1794) also moved to Simpson Co MS.I believe he was married twice but haven't found the records.I also believe that he died between 1842 and 1849 in MS.
4) Nancy's family remained in the area and records are available for them, in addition to Mrs. Stevenson's book.
5) According to what I have found, Patience Floyd Garrell (Gerrald) lived in Horry County.
6) Wright, sometimes listed as Right.
7) Anna Jane Floyd married Isaac Mincey and lived in Horry County.
8) William Everett Floyd md 1) Nancy _?_ and had at least one child, possible 3.There is a tombstone in the Floyd Cemetery near Mendenhall, Simpson Co, MS for "V. A., wife of A. J. Woolsey, Dau. of Everett & Nancy Floyd, born in Ga Feb 13, 1836, died in MS Jun 2, 1899. William Everett Floyd md 2) Martha Jane Ware on 20 Apr 1837 in Randolph Co GA.They moved to Simpson Co MS ca 1854 and settled on Strong River north of Mendenhall.
9) Hardy Floyd died 1 Jun 1845 in Randolph Co GA. Some of Hardy's family moved to Barbour Co AL.
10) Mary Floyd married Elias Jernigan.I believe that she was born ca 1794-1804.
11) The 1791 Frederick Floyd who md Sarah Pitman appears to be the s/o James Floyd (died 1828) and Elizabeth. The 1814 Frederick Floyd seems to fit the family of Frederick (b.~1769): A. We know that Frederick (1769) had a son named Frederickfrom the probate records. B. Sarah Floyd, Widow, had 2 sons un 10 in the 1820 census. C. Frederick, s/o Frederick, dec'd, bought his land at auction in 1842/43 (not 1854). D. Frederick (1814) first appears on the Horry Co Tax records in the mid 1840s.