Let's see if I can clear this up without exposing anything. It's a tough thing to do.
Okay, an expanded shell can generally be used with a normal sized coin. Much of the time you can use it in conjunction with normal coins that are in circulation. This isn't the case for every expanded shell but is generally true.
The non expanded shells usually require a specially made coin that will work with the shell. If you lose this coin then your shell is virtually useless.