The names on grave stones are proper names for a time, while the memories of survivors provide reference-fixing context. But with the passing of the survivors the names revert to commonality. After a while the dead may as well lie in a common grave.
What lies below the stone is not Patrick J. McNally, but a Patrick J. McNally. And not even this; rather, the bodily remains of a Patrick J. McNally. The person has fled or no longer exists.