You wrote: Anyone can just add a grave to "Find a Grave".
I believe you are wrong yet again. It has been my understanding that one can ONLY add a grave to Find a Grave if and only if one is absolutely positive that the individual is buried in that graveyard.
Which is most definitely NOT the case in the Robert Abernathy 1 that you found. I found him a couple of months ago, and knew at once that those who erected the memorial stone had not had the opportunity (or desire) to search out the evidence that Margaret Ogilvie and I have.
Fact: Our Robert was 19 years old when he arrived in the winter of 1651/2. His passage was paid for a Robert West (along with several others) and his bond servitude contract was purchased by one George Armstrong. Because of the statutes then in effect and his age, he was required to serve as an agricultural bondservant until age 25, whereupon he would become a free man (which also allowed him to marry his sweetheart and mother of his daughter as of 3 May 1657). The "Cow Document" was to guarantee said daughter a dower at the time she intended to marry. A practice that followed Scottish rather than English law of the time period regarding providing for "natural" children.
I would write more regarding the sources of the above fact except that at the moment the small of my back is much too painful because we're trying desperately to rid our property of a pernicious weed before it goes to seed and we have ten times as many of them next year.
I suggest you google for Merchant's Hope Cemetery in Virginia and zoom down on it. The Cemetery attached to that Church on Merchant's Hope Road is the exact same 100 acres originally purchased by Robert (1st) in 1664, having been donated to that church long after his death by someone into whose possession it had come.