Never look at a tombstone in isolation. Make a note who is buried in close proximity to your ancestor–it could be someone with a connection. A different last name on a nearby stone could be a married sister, a mother buried under a different husband’s last name, an aunt or uncle, other relative or close friend.
It is also possible that someone purchased eight spots in a plot of graves and, after years of not using the “last spot,” let someone totally unrelated have it or later sold it. The cemetery may (or may not) have those records.