i'd sue the person that sold me the invalid ticket..yep yep..The laws don't dictate when the ticket can be valid. They do however dictate conditions of sale and false advertising. The person trying to USE the ticket isn't breaking the law; they're just going to be turned away at the gate.
The person selling that used ticket IS breaking the law. They KNOW that the ticket is not going to be able to be used, but they are putting it forward as a valid park ticket that can be used for entry. That's called fraud, and it's against the law.
If I run a travel agency, I can sell NEW Disney park tickets. I can't sell tickets that were already used at the gate, and tell my customers that they will be able to use them to get into the park. You can't sell something knowing full well that the item can't be used as advertised.
So if I try to get into the park with an invalid ticket and I am turned away, no, I can't sue Disney. I can certainly sue or press charges against the person who sold me the invalid ticket because they broke the law.