Its possible the headstone doesn't exist. Do you know where they lived? Did family stay in the area?
The IOOF Cemetery in Farmersville has a Coke C Prater 1869-1945; Jason Scott 1893-1972; Virginia no dates. Farmersvile Cem also has a Morris Prater d 1938 CSA. (1920 census says he was abt 1886.)
Nevada Cemetery has Josie 1858-1935; Juliette wife of RW 1837-1903; RW 1833-?
In 1880 they lived in Pct 7 which is the area the two above Cemeteries are in or close to.