OK, some results: Before shutdown -h I checked with Fn End that I was already in the dimmest state. However, at the next power-up, sitting at the Lilo prompt, I could use several Fn Ends to make the screen dimmer. Well even though it seems brightness is not remembered through cold power ups, at least nothing from then on until shutdown made the screen brighter. (I did not test reboot(8), but instead a cold power up.)