PJ to PJ, yes, but if you're comparing the inlay versions of each they're pretty different. I really prefer the layout of the 21 inlays, they just flow really well. They also look more symmetrical between sides, and the gap between them falls right on the pad of your fingers and gives a better grip. Also, the 21 was the last to have mammoth ivory as an option.
Other than that, main difference is the bushing system and Ti on steel lock. The bushing is really nice because it's always smooth and you can tighten the pivot down enough that it won't come loose, no fiddling or loctite required. It has a unique feel to the action and not everyone prefers it. But if you're one of those people, it's really hard to find anything comparable. I'm guessing the matching and hand-fitting of bushings ended up being too costly in the long run.