Just FYI, A good way to tell the generations apart:
Gen 1- flat grip all around with rough edges
Gen 2- Checkering on front and rear straps of handle
Gen 3- Finger grooves added, accessory rail, loaded chamber indicator
Gen 4- interchangeable backstraps, different grip
These are only the cosmetic differences that immediately allow you to tell the generations apart. There are of course mechanical differences as well among the generations.