if the casino can immediately declare them worthless?

If a thief steals what he thinks is a million-dollar painting, and it's really just a $200 reproduction on display while the real one was being restored, he can only be charged with stealing $200 worth of goods. He might be able to be charged with attempting to steal more, or with conspiracy to steal more. Or maybe they will argue that, at the time of the theft, he actually did steal $1.6 in value (although the value went down immediately after that).

These are the questions that make me wish I was still teaching law school and presenting students with "what ifs."