I'm digging out my Birthright materials again, ... I have all but
about half a product (I didn't get the naval rules box, but I have
Cities of the Sun) and am a bit rusty in finding things.

In various places it mentions fairly clearly how many mages there are,
and what percentage of the population is assumed to be going-up-level
classed characters.

Can someone point me towards references before I reread Everything?