I think the answer is "they're all like that". I looked at about 10 1881-O and a couple other years/mints on Heritage and they all have it. The M has some too. Must be from punching a master die.

I've noted this on Barber dimes - the E in America has evidence of tripling at this magnification, and it occurs across all dates.

I've noted this on Barber dimes - the E in America has evidence of tripling at this magnification, and it occurs across all dates.






















