During her run on the series, Elizabeth Keen's birthday, in particular the birth year, was always close to that of the actress who plays the role, Megan Boone, which is 1983, yet the gravestone is engraved with 1985, a two years difference.
When Elizabeth visits Tom's grave in Season 5 episode 9 "The Ruin", it shows a particular headstone behind and to the left of
Tom with a last name that ends with the letters "azza". In this episode, that headstone has disappeared.