I would call in personally, and use a bit of charm stating you know your persons burial details and plot number,and wonder if there is any one else buried with them,the person may just look up for you on the spot ,other than that you would have to sit and cross reference every burial in there to find a person with the same grave number ,it would be over quite a few years,so unless you have a rough idea who may be in there ,you have a very difficult task,
would you like to post possible names and dates here so people could look up their burials,
I wont promise a result ,but its free.