That is actually a legal question. Of all funerary monuments from before World War II, we can assume that there is no longer any obligation for relatives to maintain the grave. In some cases the families have even died out. Because not all burial registers have been preserved and not all grave monuments are equally legible, it is often difficult to trace next of kin. Even if a family wants to take care of the maintenance out of involvement with the heritage, it is not always known where the ancestors are buried.