A left and right page original drawings set is a collection of two drawings that accompany each other in the book, Now You See It, Now You Don't. For example, when the drawings Say When Pass I - Left Page and Say When Pass II - Right Page are together, that is considered an original drawings set. If you were to add both of those items to your cart, you would then receive the associated $100 discount from your cart total.
As stated in the previous answer, if you add both original drawings from an original drawings set to your cart, you will receive the associated $100 discount from your cart total.
Yes. Each original drawings set carries a $100 discount, so for instance, if you were to buy the Say When Pass original drawings set, as well as the Come Back Coins original drawings set, you would receive $200 off of your cart total.