I think we should be able to send an explation for why we did use the T/O rule in our games. As a remainder to our opponents. It feels very tough to claim a T/O on a player who did not even know that the tournament had begun.
I think it's always tough to claim a T/O unless your opponent has just quit playing. It's especially tough in the situation you bring up Harri. That's why I think T/O should be automatic in tournament games. Then, no explanation would be necessary, nor would the tough decision be forced upon you. Unless that happens, you could always use the "e-mail opponent" option to explain why you're taking it before you actually end the game.