I was wondering why would anyone carry a magazine with 12 or 13 rounds (or 12 + 1)? Turns out, with the help of Google, there is a Glock 12 round magazine: https://themagshack.com/shop/pistol-magazines/9mm/glock-g26-9mm-gen-4-12-round-magazine/
Ya learn something new every day (hopefully).
My duty weapon was a Glock 19, it had 19 rounds in the mag.