The spring in the wheel cylinder between the cups makes the residual valve in the Master cyl, redundant, not nec.
So, if the wheel cyls have a spring, you don't need the residual valve in the m/c.
That makes no sense. They have ALWAYS had springs. I was taught that drums need residual, disk do not. There are sometimes exceptions, I was told depending on master cyl. location, IE older vehicles under the floor boards.