If I decline a game and then reconsider for any number of reasons later on,
I'm in, so long as the game has not started...

If I decline a private tournament and then reconsider...
no dice, regardless of whether the tournament could possibly have started yet... :-/

Anyone know why?

maybe you don't meet the prerequistes in the tournament

Possibly, the invitation limit was reached. (if someone declines, you can invite another player to replace them, which could lock you out of the tournament, I'm not sure how that works)

In open games everyone is invited.(exception prerequistes) When you join game page, game ask you second time, Are you sure? You might want to check game settings. If you want to play you can join. İf you left, you can came later and join again. İts open for everyone.(exception prerequistes)

But when you take invitation for tournement, that is your only ticket. İf you decline ticket you do not have any more ticket. But solution for this is simple. You can ask from host of tournement to sent you second ticket. İf host sent you invite again, you can join the tournement.

This is same for alliance invitation. İf you do not nothing invitation stays there. But if you decline you do not have invitation anymore. But after you decline you can ask to recruitier from alliance to sent you second invite. İf he sent you invite again you can join, or decline.

Edited 10/26/2015 10:57:44