Over polishing the fields can reduce the size of devices. I found a 1962 proof cent reverse where the coin was normal except for one area where the word UNITED was polished. Perhaps die damage and polished to remove it:


here is another example on a 1968 cent that was over polished on the "1" in the date:

But as mentioned above, it was probably a weak punching of the mint mark.
Edited by coop
12/16/2013 10:49 pm