> they're either marked or not They were marked when Ivy's assistant asked to turn the 9s around 180 degrees. The design on all the cards was identical; it's

> they're either marked or not They were marked when Ivy's assistant asked to turn the 9s around 180 degrees. The design on all the cards was identical; it's not as though face cards had a different pattern on the back. The design just happened to be very slightly asymmetric so that turning the 9 cards served to mark them. If you were not able to turn the cards, the asymmetric back would provide no information.