I've even seen the weird combination of the client and server both authenticating, but the account owner being given a choice if they want to 'level up'. It essentially means your public reputation and match history (and actual experience) no longer align.

I suppose that matters less if we're doing checks on the actual data, but for the player base, you cannot rely on what the game reports about the experience of your opponent, which makes for very confusing matchups (and the accusations that go with it).