Not sure what you mean by "Oops." I've done dozens of pad changes on these types of Girling calipers, even rebuilt the calipers themselves. Never had any trouble...although the Centric ceramic pads I just installed were a bit of a tight squeeze. But all the pads I've ever seen, of any manufacture, including Volvo's, have this notch.

They don't have anything to do with the anti-rattle springs as they are too far offset from the center of backing plates edge. And they're oriented so that one notch is always up and one is always down.

Again, they must be there for a reason, one that has nothing to do with any of the many Volvos I've had and re-braked. Just curious if anyone knew why?