The variators are different.. if you look closely at the front ramp plate of the PA50I, you'll see that it's curves do not curve inward as severely as the plate on the PA50II. and there are other differences you will notice if you take them off and compare..
If that front pulley is unable to close completely becaue of rust on the shaft or something, top speed will be lower.
Another thing on old units is the internal parts can get really messed up and worn down. The weights inside and the plate-ramps they slide on need to be perfect. If the rollers are prevented from traveling all the way out , the pulley will not close all the way. When those weights are thrown outwards they actually push on the inner plate and move it inward.
I have a variator that's worn badly inside.. the little ramps that the weights roll on are practically gone. Although the weights are thrown outward by centrifugal force the plate hardly moves.