The 35mm f/2 AI-s used 8 elements in 6 groups. The 35mm f/2 f/2 AF-D used 6 elements in 5 groups and focused a bit more closely. On many "consumer" level cameras, both film and digital, AI-s lenses will mount and shoot, but only in unmetered manual mode, which is about as much "basic dark ages" as using a 35mm f/2.8 PC. Unmotorized AF and AF-D lenses will not provide autofocus operation on D40, D60, D3x00, D5x00, and D7500 camera bodies. The AI-s lens can only be used in program mode with the FG, FA, and N2000/F301 and only in shutter priority mode on the FA and N2000/F301.
Nikon also has 2 current 35mm f/1.8 lenses and a 35mm f/1.4. One of those 35mm f/1.8 does not fully cover the 24x36mm film or "FX" frame, the other does. All three lenses are essentially unusable on manual focus film cameras, and can only be used on cameras like the F4 and the N/F90 in program and shutter priority modes.
Isn't Nikon "compatibility" wonderfully simple?