I see what you are saying, one dot.
2 possibilities, maybe: 1-that blade was put in the frame at the factory after the 3220 was reintroduced, a blade that would have been good for any other handle material except for the yellow Delrin or 2-the blade has been replaced either by Case or a knife mechanic. Unless you've owned the knife since it was NIB, you never know what happened to it for sure. A factory repair for a broken clip doesn't guarantee the replacement blade to be from the same year.
Probably there are some other possibilities, maybe someone will help solve the mystery.