I see references to "brightness" in here.
It's true that ISO is an indirect control for brightness (especially in the case of the pushed / pulled back ISOs), but this is not ultimately useful, unless you don't care about making large prints, or you need the brightness set out of the camera (in fact you don't). If you do any post-process work at all, however, you don't need to slave to make brightness "correct" in camera.
Instead, if you want to get the most out of every pixel, you ought to overexpose the shot (i.e. dial in 2/3 stop overexposure or whatever your camera needs) to pull as much shadow areas into the first half of the data as possible.
There will be less noise in the shot (especially in darker areas), and the RAW will be larger (more data to play with). Pulling back brightness in post will not add noise, of course.
As always, there's a good, practical guide to this, found here (Luminous Landscape)
. There are also some comments about camera makers and film camera era thinking, which is not worth beating yourself up about or trying to make sense of in strict film camera terms.