Spent is from the transmitter's perspective. Coins aren't destroyed, they are just moved around.
If I send all my coins to an unused address of mine, there's no way to tell if that is me or another person. If later I send them back to the address that was known to be me...
Then you know I have them, but you still don't know if I sent them back there, or some other party did.
You are thinking that, since it's easy to list all the possible chess moves in the next move, that you can tell for sure how the board got in its current state after 100 moves.
