When Gilly Hicks launched (subsidiary of A&F), one of their main selling points for the stores was having all of their bra sizes and styles available in the dressing rooms. Thus, you could go into the dressing room to figure out what fits, then pick out the ones you liked from the store floor.

I'm not sure if this is still the case, since I no longer work at A&F and don't go to Gilly Hicks, but my coworkers at the time were pretty excited, since finding well fitting bras can be very difficult.