I know the P99 was the first gun with replaceable back straps and first striker DA/SA with decocker
But there was one more. I can't find a definitive source for when the CZ 110 was released. The CZ 110 was the DA/SA version of the DAO CZ 100. Both the Walther P99 and CZ 110 were released in the same era, when pistols had proprietary accessory rails, both were DA/SA striker fired pistols with decockers, and both had a "SA-trigger-forward" mode of the trigger that was only accessible when racking the slide without a trigger pull.
The CZ 110 definitely had an "AS mode" even though CZ never called it that. A quick scan of the online instruction manual does not even mention this mode of the trigger:
https://web.archive.org/web/20071218053849/http://www.czub.cz/navody/cz110_en.pdf
But a look at this video (in Spanish) clearly shows that it is there:
https://www.youtube.com/watch?v=eK3VGYruZNg
The reason I bring this up is because I believe it is related to the thread topic. Personally, I don't believe Walther set out to create the AS mode of the trigger. I believe it is simply a byproduct of making a DA/SA striker fired pistol.
On a hammer fired pistol, when the hammer is cocked, it pulls the trigger to the rear because it is physically connected to the trigger through the trigger bar, and all three are in the frame.
On a striker fired pistol, the striker is in the slide, and the trigger and trigger bar are in the frame. It would probably make things difficult, and/or overly complicated, to design a striker fired pistol where the trigger moved to the rear when the striker was cocked, and I believe the "AS mode" is only there because of this.
Why would the only two manufacturers that made the only two polymer striker fired pistol designs that used the DA/SA trigger action, design both to have a "SA-trigger-forward" mode of the trigger? Walther created the DA/SA trigger action, and they never used an "AS mode" in any pistol before or after the P99 was released. CZ seemingly never even mentioned the existence of this extra trigger mode.
The point of the P99 was to create a striker fired pistol that mimicked the trigger action of a hammer fired pistol. For the most part it accomplished this, but with the addition of another trigger pull that doesn't need to be used unless the slide is cycled without pulling the trigger. I'm pretty sure Walther meant for the P99 to be carried decocked, like practically all other DA/SA pistols.
I owned my P99 for around a decade, and tested out both the DA and AS modes, and I found that the difference in time between firing the first shot with both the DA and SA modes were negligible. So I chose to go with the inherently safer DA trigger mode when the P99 was my carry pistol. I also liked the fact that the decocker on the P99, while pressed and held into the slide, acts as a "striker block", and the cocking and release of the striker will not cause a discharge while the decocker is pressed into the slide. I made a habit of pressing the decocker when holstering.
