Glock like most firearms has evolved there design over the years this is the "Generation" Glock divides there pistols into models referring to size and caliber so a Glock 17 is full size 9mm well a Glock 22 is the same size but .40Sw Glock 19 is a smaller 9mm well 26 is the smallest in the same. well 34 is the long slide Glock 17.
Generations cme in referring to other changes made. Even if the caliber and model didn't exist prior to when the "Generation" was started it falls into this
The mechanics have remained more or less the same but each generation is an improved design.
Gen 1 glock were the initial production back in 1982.
Gen 2 introduced in 1988 They refined the grip and Slide release, They also added the Steel plate to the dust cover to meet US ATF regulations allowing import to the US, a feature visible on the Norinco frame and changed the floor plate of the magazine and changed the recoil spring. Taiwanese t97 pistols were inspired by this design with the addition of a slide mounted safety, a feature Glock has added to it's pistols for use by armies that demand such.
Gen 3 1998 The Glock rail was added ( not the same as the industry standard rail ) A feature visible on the Norinco frame. The grip was changed again with the terrible finger grooves Which are visible on the Norinco marked frame, they also added the Thumb relief and there were there changes to the internals ( also on the Norinco)
Gen 4 in 2010 They reduced the size of the grip, a long time complaint of the pistol due to its "Block" like profile, They changed the texture of the grip which is close to that seen on the Norinco pistol. Glock pistols introduced modular back straps on gen 4 to allow the user to scale up or down the grip a feature not apparent on the Norinco pistol They also changed the recoil system.
Gen 4M 2016 as minor upgrades for the FBI and NYPD In some ways a prototype for the Gen 5.
and Gen 5 2017 This is the latest Glock iteration, They got rid of the finger grooves, Ambi Slide stock, Changes to the surface coatings of the barrel and slide, New Refilling, Flared magwell with moon shaped cut outs, redesigned magazine floor plates
So that all done We look back at the pistol frame with the Norinco marks, It has a lot of features form the 3 frame with the texture of the 4. Since the pistol is incomplete we can't comment on the slide but the control spaces are there and match a Gen 3 Glock.