The older 1950's vintage cast iron ones had larger bushings that never seem to wear. As time when on Pontiac discovered they could cut costs by using shorter bushings. These later distributors can have slop in the bushings usually caused by poor maintenance of the engine over time.
The earlier distributors for the most part have more accurate machining of the lobes. Sometimes on later ones the lobes are not perfectly 45 degrees apart.
For example what we have noticed is that a distributor can have #1 & #6 lobes machined exactly 180 degrees apart. Then #2 & #3 are 180 degrees from each other but, are they are machined 46 degrees from the previous lobe.
Then #4 & #7 lobes are machined 46 degrees from their previous lobes but still 180 degrees from each other. The addition degree in both lobes pairs makes the #4 & #7 92 degrees away from the #1 & #6 lobes.
Then the machining process somehow detected the error and the #5 & #8 lobes would be at 43 degrees from the #4 & #7 lobes and the #6 & #1 lobes. That would ensure that the #6 & #1 lobes would be machined perfectly.
This isn't something that would be noticeable to the average motorist. I am guessing that at some point GM lowered the quality standards for the lobe machining in order to save some money. Hard to believe that would happen.
This is a difficult to explain subject but it is as clear as a bell when testing on a distributor machine. You can get a idea in the video by looking at the flashing arrows around the distributor. The presentor in this video never checked or mentioned anything other than the #6 lobe.
https://youtu.be/fh0jXS1p3bY?si=iCXyqyF8DOVr2M47