When visiting a cemetery, I always make a beeline for the outer edges, the fringes, the periphery of the property. As often as not, I find "lost" graves that have gradually been forgotten by all.
It usually starts when foliage on the edge of a cemetery is allowed to begin to overtake graves nearby. At first whoever mows the cemetery is aware of these graves, but they lazily stop mowing around them because of the overgrowth. Years later, someone else is mowing the cemetery and doesn't realize the graves are there. Decades pass and they end up becoming completely obscured as the woods and shrubbery move the outer border of the graveyard inward by several feet.
I estimate that in the last decade, I've rediscovered 200-300 "lost" graves back home in Kentucky cemeteries. They may have been listed in the cemetery records (or they may have not if the lists were compiled after the graves were covered up) but they were completely invisible. From the looks of them, many had not seen the light of day since before my lifetime.
For example, recently in Gulfport's historic old Lincoln Cemetery I was puttering around the far corners and came upon this grave marker well on its way to being lost. Covered in leaves and debris that's been piled up on it and around it, only a tiny glimpse of it peeked out and caught my eye. Sure enough, I cleaned off all the leaves and found there's a grave here, and deserves better treatment than this. Still more lurk forgotten and neglected in the further wooded outskirts of the cemetery, I have no doubt.