Old Abe picked some boogers and wiped them in the recesses of the letters and on his chair, too! In other words, grease & debris accumulated in the die. Chris
I am seeing a couple of things. The die is getting old and worn (the FG and the die deterioration doubling on the letters around the rim), and in order to try and clean up some of the die deterioration the die has been heavily polished resulting in the thinning of some of the lettering (Most noticeable on the E Pluribus Unum).
