Perhaps we are on different pages. Once an image is digitized, its digitized. It has a fixed bit depth. In the case of modern DSLR's, the 14-bit output of a RAW is fixed,
The part that you seem to not quite get here is that if you have a noise level of "8" and your scale goes from 1-16384, you don't really have 16384 distinct levels in your output signal. Nor do you have 16384 - 8 levels. You have 16384 / 8 levels (2048).
however since it is in the "lower order bits", or in the darkest tonal levels of an image, the gain is minima
. Were not talking about a huge difference overall, we are talking about a very small difference overall.
I don't think you understood my previous post. Losing the lower order bits is equivalent to throwing away the bottom two bits. If you throw away the bottom two bits, you don't subtract the lowest 4 points from your range of values, you essentially divide everything by 4.
But anyway, this focus on number of levels is a big red herring, because as we all understand well, dynamic range in the highlights is interchangeable with dynamic range in the shadows. A stop of dynamic range is a stop of dynamic range (and a stop of dynamic range in the shadows can be a stop in the highlights if you want it to be)