I think the OP did much butter so far by NOT asking for the official policy. I don't think that upgrades to a suite or multi-level upgrades in general would be covered by any official policy.
Likewise, while buying Ambassador will guarantee him a one-level-upgrade, he'd probably not be getting multi-level upgrades in the future. I'd still join, though, if staying at ICs more than one or two times a year.
HTB.
Actually, after further thought....I agree completely. These upgrades are indeed pretty good. I would just put on my best charm and try to check in with the agents that get to know me and hope for the best. I would sign up for Ambassador as well as I might even give them more leverage in giving better upgrades more often.
My policy though is to check before I go to a hotel so I dont leave anything to chance. I do agree with you though that in this case the OP probably did better than anything the hotel would state as offical poicy.