There aren't any official gens. You can have later "gen2" serial guns with a mix of "gen1" parts. The only way to ensure you have the latest version is to find one with a reversible mag release button.
CZ rolled out a series of changes after the initial release. The first part that was updated was the front locking block. A metal tab was added to prevent the slide stop spring from popping out. They also radiused the the bottom rear corners of the block where some trigger bars were rubbing.
Some people had ambi-mag releases where the mags would stick if the button was held in tightly. CZ removed a little material from the back edge of the catch.
The next major change was a square notch cut into the slide to prevent the striker housing from rotating and allowing the cover plate to drop down and hang on the back of the rails as shown below.
Here's the square notch to the right of the cover plate.
Fortunately, older models can be updated. The front locking block is a straight swap, the mag release catch can be fixed with a few file strokes or sandpaper, and Primary Machine can cut old slides to use the new striker housing for $60.
However, the latest change is the switch from the ambi-release to the reversible release. The frames are molded differently so there is no way to convert one to the other.
