There have been Best Buy employees here who have already said this... and I have friends who work for Best Buy as well (one is a Shift Supervisor for Mobile).
They cannot fulfill every preorder. The "get it a launch" doesn't change... It just shows the date the phone will be available. They have no idea how many phones they will have neither.
If last year is worth any comparison, they had 2 iPhone 6 pluses for AT&T and Verizon each, and thats it. So some might get lucky, but I feel that if you're betting on a store thats not Apple or a Carrier to get your 6S+ be prepared for a major let down.
More iPhones for us though!