Hi Jo...this is not an error, but a very good strike. What is unique about this in the series is that is has the .999 on Both Sides. The older Gold Coast CT mints have a variety of 4 different slot machines and two each of the other designs. The one you have is the good one and usually sells between $300 and $500. Often overlooked and identified by the "Limited Collector's Series" the .999 Both Sides is the significant feature. Other Casinos issued strikes with the Collector's Series, but not the .999 Both Sides...regards..Peter