Just spoke to a rep who works directly for the Presidents Office of AT&T
I filed a BBB complaint against AT&T for how they handled this whole multi-window update fiasco. Someone initially contacted me the other day, and I missed the call. They attempted to contact me, again, and I missed the call. And then another time. Finally, I was able to get them just about five minutes ago. They told me they worked in the presidents office at AT&T. He wanted to inform me the update for multi-windows was, in fact, out as of the 27th. I told him I was aware and had updated.
I took the liberty to inform him of the issues a lot of you all were having. I told him that I had to do the date change trick to force an update. I told him there were many people posting online, of having to wait crazy amounts of times (like 2,800 hours) before being able to successfully check for an update. He gave me the usual mantra of appreciating my feedback, and he'd give it to the folks in-charge of the software development and the people in-charge or rolling out the update. He also told me the reason why it took so long for AT&T to release the update (and he was quite aware AT&T took the longest of all the carriers) was because they do extensive testing to make sure things like multi-window will be compatible with their network and whatever else. So, take that as you will. I know another rep from retentions told me the exact same thing. I don't necessarily think they're lying about that, but I'm sure there's some underlying things we are not privy to.
At any rate, I also asked him how the update was released so I can pass the information along to people on sites like XDA and others. I wanted to know was the update a staggered release or should it have been available to everyone at once? He told me that from what he was told, the update was INITIALLY staggered, but as of right now, EVERYONE should be able to update to 4.1.2. So, there you have it. From the sheep's mouth. I hope this information is helpful for someone. I will post this on a few other websites I'm following pertaining to this same issue.