I don't remember if the 2 pin to 3 pin change was gen 1 to gen 2, or gen 2.5?
3 pin frames began with late Gen2's in .40S&W and early .357Sig. 10MM as well.
It became standard on all frames with Gen3's.
My Glock Gen 2.5 is a 10mm. It has 3 pins. It has finger grooves and stippling in their positioning on the grip that split it between a Gen 2 and a Gen 3.
