Glocks
I just read a bit on Glock "generations" recently. An online search yielded a pretty decent article complete with pics on the Glock "gen" topic. Gen1 Glocks, if I recall correctly, are limited solely to the G17 platform. They are relatively rare and I'm not so sure that many made it to the USA. Seems I read elsewhere that Glock made a run of retro G17 pistols that mimic the gen1 pistol to some degree in the recent past, but I am not certain about details, my memory is sketchy on the matter.
Gen2 Glocks are what many shooters label as Gen1, but they are not. The Gen2 pistols have no finger grooves on the grip, and have no rails. The checkering on the grip is different from the Gen1 G17 pistol. """Note that a variety of other Glock models were introduced in this era, but they are Gen2 pistols, but the first iteration of that model.""" Technically, they are still Gen2 Glocks.
Gen3 Glocks got rails and finger grooves. It is important to note that up to and including the Gen3 pistols, Glock did not mark the slides with a generation marking. The Gen4 pistols received the first slide markings of "gen4" throwing Glock fans into a tizzy ever since.
Based on the description of the G30 you are considering, and its lack of a dustcover rail, I would label it a gen2, ie, an early G30. The grip should be devoid of finger grooves as well. Note that Gen2 and Gen3 slides and frames will interchange within frame sizes. My gen2 G20, will accept and function with my gen3 G21 frame and vice-a-versa, and to me the gen3 frame feels slimmer and less clunky than the slab sided big frame gen2 models.
Disclaimer, ......this is all from recall on an article I read about a week ago. I've slept many times since then
and may not have all the facts exactly right, but I am fairly comfortable about my recollections. A bit of online searching and the same article with pics is still out there for review by all.