Just to clarify, I hadn't "missed" the game, it was upcoming, but on a different day than I wanted so I was able to easily trade my ticket. I could certainly see why the Nats wouldn't let you trade tickets for a game that had already passed.
The policy is no exchanges for any game other than season ticket plan tickets, this includes red carpet reward tickets and rain check tickets. I'm surprised that this was allowed and wonder if it is repeatable.
