A lot of old churchyards have removed old headstones for safety, they often place them around the boundary wall. I have several photographs of the area where some of my family are buying but all there is to see is what appears to be a lawn.
Then just because a burial is recorded in a cemetery it doesn’t necessarily mean there was ever a headstone. Many families couldn’t afford one.
Many people have been exhumed and re buried elsewhere where when churches have come to the end of their intended use. That happened about six years ago at the Church where I was married. The church is now a house and the bodies have been removed to a municipal cemetery. The headstones (not all had them) can be seen along an old boundary wall.
To give an idea of the reality - our church's register goes back into the 16th century, and records just under 10,000 burials; the church is significantly older, so we think we may have another few thousand. We have records of more recent graves, although the location of each grave wasn't recorded in the register until the 1990s. We have about 700 headstones, of which about 100 from dates up to mid 19th century were moved to the perimiter of the churchyard in the 1990s. I haven't counted the number of grave plots that are visible (i.e. headstone or unmarked plot between two headstones) but I'd estimate at around 800. And to make it more complicated, part of the churchyard is an extension from 1930, so the original area must have been re-used multiple times.
So when I'm asked to locate a grave, often it's totally impossible if it's from before about 1900, as there is neither a record of where it was, nor is there a headstone. For 20th contury graves that don't have headstones, we can make an educated guess by burial date - but our evidence is that graves weren't always used in sequence (it's possible to reserve a plot, for example). So I've had to give disappointing replies on occasion, with no hope of answering the researchers' questions.