I've shrunk 2 over the years and kicked them back, BW usually goes hand in hand with cheaper fitting and cheaper clients. A fitter I know has a letter in his van stating that BW has to have double gripper rods when fitting (this is an insurance policy for the supplier) but who's going to pay for that?
BW is fitted by cutting it to the shape of the room there's not much excess for stretching as it can rip, luckily for me approx 1/2 inch was an easy one, a guy in Manchester area has the record of 7" shrinkage so I've been told.
Shaun