The letter designation grades are redundant

Why are letters used when grading a coin? The number provides everything you need to know, doesn't it? I mean, who ever saw an MS40 or AU65 coin? If the coin is a 65, then it's MS, right???
When I was a child, I caught a fleeting glimpse
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<< <i>If the coin is a 65, then it's MS, right??? >>
bwuahahahahahahahahahaha!!!
ever looked at slabed ms-65 bust coins???
bwuahahahahahahahahahaha!!!
K S
or the SMS coins. The letter designation states which coin is MS,PR and SMS.