[DannyR]

There was never a Gen1 framed G21 made. Gen2 frames have no finger grips or accessory rail. Gen3's do. Gen4's have interchangeable back straps and dual recoil spring assemblies. Gen2 & Gen3 G21's share internals.

 

[DannyR]

The Gen1 frames were produced from 1982 until mid 1988. Prototype G19's were built on Gen1 frames in early 1988, but the production G19's were on the new Gen2 frames. The G20, G21, G22 & G23 were introduced in 1990, all on Gen2 frames. In 1997, the G29/G30's were the first pistols with Gen3 frames, and others followed in 1998. Gen4's started to become available in 2011 and are presently available in G17, G19, G21, G22, G23, G26, G27, G34 and G35.

 

[DannyR]

I must be tired to forget my 2nd favorite Glock, the Gen4 G37.:upeyes: