"I do not think a grading system would work for strikes. There are too many variations in every strike made." .... Sarge
'Variations' has nothing to do with grade... it has to do with die variations or striking characteristics as minted.
Grade has to do with condition of coins or silver strikes resulting from circulation wear or damage. Relatively very few silver strikes are affected by wear as they are generally protected by the plastic capsules they are usually housed in and do not circulate outside their plastic holders for the most part.
Discoloration due to exposure to atmosphere is not wear. The silver strike can still be described as uncirculated, but discolored or 'toned'.
