This thread is a wonderful resource. Thanks for creating it.
I can contribute some information about the 45ACP and 10mm subcompact pistols, models G30 and G29, respectively.
I have noted owner/buyer reports and data in the Glock Serial Number Research Project
database showing the Gen 3 versions of the G30 and G29 subcompact pistols went through a transition from Gen 3 models without an accessory rail to later Gen 3 with the accessory rail.
Before the accessory rail was added, G30 and G29 pistols were manufactured that had all the Gen3 characteristics:
- Finger grooves on the front strap
- Checkering in the finger grooves on the front strap
- Thumb rests on the grip
- Three frame pins
- Loaded Chamber Indicator Extractor (LCI)
Therefore, I do not think it correct to assign an informal designation of Gen 2.5 (a designation that Glock, Inc. doesn't recognize officially) to the G30/G29 without an accessory rail. I believe it's more correct to simply describe the two variants as "G30/G29 Gen3 without accessory rail" and "G30/G29 Gen3 with accessory rail."
The database indicates the accessory rail first appeared on the Gen 3 G30 45ACP around June, 2005 with serial number prefix HGM.
In the database, the first record for a Gen 3 G29 10mm specifically mentioning a rail has a test fire date in February, 2006 with serial number prefix HXN. It's possible that the Gen 3 G29 had an accessory rail earlier than this date since the G29 and G30 share a common frame.