Back in the day of punching digits into the dies either singly, in pairs, or with a three or four digit "gang punch", it was possible for a Mint technician to orient a punch upside down or in a position other than would be proper on a die.
They would then invert the punch to correctly add the detail to the die. The result would be a corrected digit or digits over another digit or set of digits that originally were punched in the wrong position. In this particular case, there are known die varieties on 1834 ans 1836
Half Dimes where at least the 3 in the date was punched into a die upside down and then repunched to correct the problem. Hence a 3 over inverted 3.
This coin is not such a coin.
It's late, did that make sense:-)
Have Fun,
Bill
PS: before people start looking for these on modern issues, this is something that stopped happening a long time ago. At this point, I can't pin an exact date on it but One of the last inverted date errors , datewise that I am aware of is an 1852 over an inverted date on a silver
Three Cent piece. Another is an 1858 over inverted date
Half Dime. Lastly, I am aware of an 1865 S, Ten Dollar Gold piece where the 186 was punched into a die upside down and then corrected.
There may be some others on other U.S. coins a little later than this, but that's about how far back you have to go.