immigration NO is not the same

Case in point;

immediate relatives of US citizens are not subject to visa quota, but they still get A#'s when they submit their 485.

2nd example,
How do you explain people with multiple A#'s when they submit 485s based on different catagories? Can a single person be occupying more than one visa quota?

Personally, I think immigration visa number simply means quota. When a number becomes available, it just mean that there is quota available. A# is a specific number assigned to your case. It may be related to visa availability, but it is not equivalent to it.