1 Gen, grip is kinda flat sided, 2 gen has griped surface, gen 3 has finger grooves and a accesory rail under frame, 4 gen has the rtf finish and chevron style grooves on rear of frame.
Gen 4 has interchangeable backstraps and a different recoil rod setup. Gen 3 RTF2 is not Gen 4.4 gen has the rtf finish and chevron style grooves on rear of frame.
Wasn't there also a version with the banana slide serrations as well? Or was that the same as the RTF2? IIRC, it was being called a gen 3.5 for a little while.
I think there was also an earlier Gen 3 which only had two pins....as opposed to the modern day gen 3 which has 3 pins



























