If it's not in writing, either as a publicly available statement or manually noted on your account, then those people only have themselves to blame for believing unofficial accounts over official policies if the stores start preventing the S7 double exchange.
I wish those people the best of luck, but I've tried multiple times through various methods to get the S7 double exchange verified from an official channel at Verizon before I go into the store in case the store doesn't want to play nice. From what I'm seeing, they are under no obligation to honor the S7 double exchange outside the 14 day window and it looks to be store level decisions that are even offering it as an option. As has been mentioned earlier, two people can have vastly different experiences even at the same store. I was hoping to stack the deck in my favor ahead of time.