and, on the other hand, I was assured by a Dublin cemetery that one of my family graves would not have a headstone because:
1. it was not a private plot as there were two many burials in it (11 listed).
2. The grave was never finally purchased by the family, although exclusively used by them, and no memorial could be added before the purchase.
3. It was in an area of the graveyard where most of the stones originally there, have by now been damaged/removed.
After confirming that two of the "single" burials for this family were indeed in the same plot, they adjusted their records so that I could find the rest of the burials in this plot and, on visiting, I found and photographed the plot and the stone. The inscription, although barely legible, indicated that the memorial was erected after the first (two) burials and added to after the third, all in the first five years after the first burial in the 1850s. There were no further additions to the memorial but the information there confirmed the parents of one of the couple I had been looking for.
Even where extensive records exist for a cemetery, as with civil registers and church records, it doesn't mean that they are always complete and correct. I was so glad that I had bothered to pursue this.