Lincoln Proof Oddity - Cud?

The die may have been polished on the edge a bit, making that area raised. (field reduced on the die, the outside part of the die) On a die attrition issue, you can see a distinct curve that tapers to an edge at the two corners.

Note the curve? That is from the edge of the die being altered on the collar. On the OP's coin I don't see this happening to form ends to like a die attrition. On die attrition, the rim moves closer to the devices. This coin does not show this. The location the rim is normal. Note my example posted.