The different mints would be the ones I think who could provide the correct info if they have kept records. I year or so ago I removed the centers from some damaged strikes I bought that were minted in 2005,2006 and some of the weighed .60 while a couple others weighed .51 so who really knows ? I don't think I am going to remove all the centers from my strikes to find out unless silver goes over $25 per ounce and then maybe I will punch out the common centers and sell the errors and real limited strikes.
Walt