I need to determine cost basis for stock. I have no idea when the stock was purchased.

My cousin's idiot husband found some unclaimed assets belonging to my grandma in the State of New York. I went through the process of becoming a successor administrator to my grandma's estate (she died in 1984 and her estate closed in 1985.) They sent me the proceeds of a sale completed in 2004 and a 1099-B for a grand total of $2170.00. I don't even know exactly what the security was, much less the cost basis. Is this really necessary?