I posted in the "Ask CGC" forum, here is the reply: "Thanks for your message. You can only enter one artist per order. Since you already have books in your cart for the Romita signing, you will not be able to add books for any other signing to that same order. You will need to complete your current order and then go back and create a new order for your next artist. You will print out a packing slip for each one and you can send them all in one box but you want to make sure each order is separated and put with the appropriate packing slip. Also, notate on the outside of the box that you have multiple signings inside or write all the artist's initials on the outside."