IMO, it's confirmed with AT&T when AT&T posts it authoritatively on their website. Otherwise, it's just playing "AT&T rep roulette", where you never know which answer you're going to get.
I've seen too many launches from too many companies (over the years) where well-meaning reps have given out information they truly believe was correct, only to have it be incorrect.
Edit: absolutely agree with your comment about it not knowing for sure until Thursday!
You're 100% correct. Right now, AT&T's website says nothing about FAN discounts one way or the other as they relate to the new plans launching Thursday. My suspicion is that if the FAN discount did not apply, it would say that explicitly somewhere in the extensive fine print. As of my latest reading of the fine print, I don't see any mention of FAN discounts one way or the other. Therefore, I am going to assume that FAN discounts will apply until I see proof directly from AT&T on their website that indicates otherwise.