This type of over inking on a digit is pretty common. I see them all the time strap hunting, kind of like stuck digits. I see them all the time as well. I put them back to work.
Very common and NAV (no added value). I found a series of them and never received a good answer why it happened. My thoughts are that one of the printing presses had the serial numbers over inking and it happened to show on the 3 rd digit.
I put together a ten-bill set of overinked digits a while back just for kicks. By set I mean each bill has a different numeral over inked from 0 to 9. Actually, took a while to find them all from circulation. I know they are only worth face value, but it was a fun endeavor. Simple pleasures!
