Yeah, I'm not sure how I'm going to handle that one. Technically, the smooth-groove fingergroove frames came BEFORE the checkered-groove frames, which would make them the "normal" Gen3 frame and the slightly modified (and now far more common) checkered-groove frames the Gen3.5. However, that's not how most folks refer to them, and the smooth-groove frames aren't very common, so the issue probably won't come up very often.
If they use the photo above to try to I.D. one, I'm guessing they will (correctly) assume that it is a third-generation frame of some sort, and that will be enough for most folks. I think I know a friend-of-a-friend who owns a smooth-groove subcompact, and I may just cover the 2.5/3.5 issue when I add some photos of the subcompact variations later on down the road. The subject might be easier to address with the subcompacts, as they don't have as many variations as the full-size guns.
Thanks for the input!