Judging from the scan, I would say the 65E grade seems generous, due to the very narrow bottom margin. I've seen many 64's with similar or better centering. It must otherwise be a very nice note, but I can't see it ever getting into a 66 holder.
As to the original post/question, often times there is very little to separate a Gem note from a 58E: a faint "wallet bend," or partial fold, excessive handling, even the wrong kind of light handling (or the finalizer thinks he/she sees something that may or may not be one of the foregoing) can get a note demoted. These types of i