I believe that at some point Apple removed the ATT account checking, and that's why they were then able to complete orders.
If you ordered at ATT, dunno. But since they were writing orders on slips of paper, they might have done the same thing, as well.
What they did was magnify an already-bad situation, which is likely going to be even worse next week.
I wound-up making a reservation at an Apple Store using the Apple Store app. There was no price listed on the confirmation e-mail, suggesting to me that no account-check was made. Other people reported earlier in the day getting confirmations with an unsubsidized price, suggesting the same thing.