727 Low-Reverse Servo Seal Question

Hi all, does anyone know the difference between the 62-63 servo and the 64-70, why to they call for a different seal. I've been building 727s and 904s since 1972 and never came across a problem. I had at least 20 partial old trans kits laying around and decided to do this trans with whatever parts I had for my budget bracket car to be used when I'm not racing the real race car. I put a 64-70 seal on the piston and it fits fine and seals perfect but I see that it's the wrong seal.