FWIW, It seems that if you were to take a circular snapshot of, say a G17 or G19, that encapsulates the slide's front of the ejection port, trigger guard, and down to the magazine release, those basic dimensions are shared by G17, 19, 26, etc. Where they differ is in length of barrel/slide, frame, and grip. So it seems that Gaston used the same dimensions in that area to base the rest of each variant on. For example, I can put a G26, 19, or 17 into a G26 open-ended kydex holster just fine. That back part of the frame (triggerguard, and aft and below) is like the foundational part of the Glock doublestack build. Kinda why the G26 will also take G19 or 17 mags. (and LPK's cover many different models. Now, I have no idea about the Glock single stackers...so I can't speak to those.