Swing arm pivots, early vs late version?

Long story but it starts with me needing to replace the rubber boot between the swing arm and transmission.

I ended up buy a compete rear end, sing arm, drive shaft, final drive, all the hardware etc. to get a boot in good shape. Parts didn't cost much and I have some spares.

I am tasked with removing the swing arm pivots in my '81 and they are not happy about coming out... and the tiny bolt hole they provide for extraction is a joke! (and not a funny one either)

My other swing arm came with the older style pivots (I am assume its the old style anyway), the ones with the large thread and nut, as opposed to the newer version with that uses a set screw to provide the preload.

My question is why did Kawasaki change this? To prevent the pivot from working loose? I would think the first version would be easier to service. Any thoughts?

Here are the two pins compared, shown right is the more common type with indexing pin, and left is the threaded type.

I think I will use the type on the left when I put it back together, unless anyone knows why that design was changed... or any reason not to?

I noticed the same thing myself a while back while swapping parts from another A1.I noticed a few changes besides the swing arm pivot points.Also the front fork pinch bolts are different and the some of the electrical connectors are different as well.Maybe they switched suppliers?Or the change in design was superior to the original?I think we will never know unfortunately Unless you go to Japan and track down the engineers(if still alive) and ask them.