Ron Guth:
For decades, this variety has been known as the 1809/6 overdate, implying that the final digit is a 9 struck over a 6. However, such is not the case, as there never was an 1806 dated Classic Head Half Cent. In this case, the 9 of the date was punched into the die upside-down, thus appearing as a 6. The error was caught immediately and corrected by repunching the 9 in the proper orientation over the previous "6". Today, the variety is very popular since it is the only "overdate" in the Classic Head series.