When I last visited Poplar Springs, I took down all the info on John, Margaret, her brother, Henry P.Blanset; Annie Clemons (John and Margaret's daughter in law), and several of Annie's children: Margaret, 1938-1950, had a marker, but John Henry, (d. 1950, at about the age of 2) didn't have a marker; and 2 other children, Martha Choline and Cecil Arnold both died within hours of being born and have no markers.
If you are looking at the "face" of Annie's and Margarets graves, the 3 unmarked graves are between them and the little road that goes through the cemetery.
There is a wrong death date. The right birth date was put on John Clemons, 2 Aug 1878, but the death date should be 21 Jan 1949, not 1976 as was put online in the cemetery listing. He died of coronary heart disease. My mother was about 12 years old at the time.
My mother and grandmother told me they thought that James Henry Clemons, birth unknown, d. 1950 was supposed to have a marker there. He would be beside or very near his mother and sister, Annie Clemons and Margaret Clemons. It could have been put up in recent years by some of his family.