I have checked my Nikon AI/AIS lenses and found although the T stop is a bit different from the mark f/stop but by the same amount for all stops. The variation between clicks are much less, 1/5 of a stop at most. Depend which camera and condition the shutter speeds generally aren't as accurate as the apertures.
I think the FA does the last look on P and S because the aperture stop down level on the AI lenses is not linear. However the aperture ring is accurate as I have stated above.