I don't think the Glock would be a good example. lol
What is functionally different from the Gen1-4?

You can reverse the mag release on the Gen4

Frame dimensions
Universal accessory rail
Slide
Trigger assembly
Extractor
Sights
Adjustable back-strap
Magazine
Spring-loaded bearing
Firing pin safety and spring
Firing Pin
Striker
Trigger Bar

There are probably a lot more differences, but that's just off the top of my head. The original BG and M&P BG are essentially 99% interchangeable. They improved nothing outside of the looks and feel. A true 2nd gen completely re-engineered BG would address the biggest problem with the gun in that it seems to light strike.

Honestly, I think they should start from scratch and make the BG a DA/SA. If Beretta does it well, that's where the market for micro 380's is going to go IMO. Might as well jump on it before everyone else does.

Accessory rail came in on the Gen3 and 4. Back straps on the gen4 and I put Gen3 trigger assemblies in my Gen4's all the time. How can they not interchange?

If you want to get technical the slide changed dimensions on the Bodyguard. I don't think you'll see a DA/SA on a pocket pistol. Lighter triggers = more chances of a ND

You said gen1-gen4

Those are the things that I could think of off the top of my head that have changed between those models.

Also, DA/SA means the first shot is DA. How is that going to increase the chances of a ND over a gun that is DA only. My CZ's have a long 11lb DA trigger on the first pull. A Beretta 92 has also has an 11lb DA first pull. If you were in the Army in the last 30+ years, I would imagine you have at least some experience with said pistol. They don't go bang on accident like a striker fired pistol.

Yeah you're right. I see where that was going and it doesn't contribute to the issue.

I should've steered clear.