I meant it the other way around. The non-reversible type A does not have this extra pair regardless of standard. But the type C is reversible and short of havin

I meant it the other way around. The non-reversible type A does not have this extra pair regardless of standard. But the type C is reversible and short of having pins automatically reconfigure based on the detected position, the only straightforward way to achieve this reversibility is to double the number of pins. So one side of the type C connector perfectly mirrors the other (but flipped for reversibility) mechanically and electrically. I'm fairly certain they are using double the number of USBSS because they're available due to the mirroring. It was the easiest way. Unlike the control channel or side band, you can actually benefit from using all the pairs for data transmission since they're already there.