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.
The residual pressure valve was designed to hold enuff pressure to keep the wheel cyl cup "lips" in contact with the cyl wall, to prevent fluid loss while not in use, - was what I was taught, and was in my Red Seal Manual.
Look it up .
Newer design wheel cyls came out with the spring, originally iirc with a formed cup on the ends to push the cup lips into contact, preventing fluid loss .
I just got thru doing a 67 Barracuda brakes, 9 inch drum
No springs in the wheels cyls.