Pete, there is some dispute over whether that D-shaped anomaly is really a far misplaced mint mark punch or just a strangely shaped crack, dent, or damage. Apparently even the CPG has listed it as both FS-501 (as an RPM) and as FS-902 (as an oddity). Dr. Wiles of Variety Vista lists it as a non-mint mark anomaly. After examining three specimens, I agree with his conclusion—it looks like a die crack to me, not a misplaced punch.
https://goccf.com/t/483456