For however many years people have been creating these online graveyard memorials, The Doctor (my Gr-Grandfather) has been said to be buried in the same plot as his father, second wife, and infant son. He was not. he was buried at see. Even supplying the exact details to BillionGraves they would not correct the memorial page. I resorted to ADDING THE EXACT DETAILS JUST LIKE THIS, and eventually someone DID alter the memorial page so it now says (or did last I checked) that he was buried at sea, and is simply named on the memorial stone. (And it's not a small stone! )
Often gravemarkers use whatever the last records give as dates, and those last records, even when the informant was a close family member, are often based on incorrect information, bad memory, or both. (I was VERY careful when giving the details for my late husband, as I didn't want some future person mentally (or literally) rolling their eyes at me (or worse) for bad information!)