My guess would be that when a stone was placed the marker was removed and discarded? There is nothing sacred about a plot marker, it's just what it is. It served its purpose and then was of no use. I see similar ones in the local cemetary where plots are for sale. But I never have inspected one to see what it was made of. I suppose lead was the easiest way to mold them if of any age as not many people had a cutting torch and steel laying around the shop back then. Monty