This is a bit of thread drifty, but not too far.

Actual concert pitch has varied a bit over the years - so when that happens, do all the people with perfect pitch suddenly find that they don't have it any more, and are out of tune, while a new set of people who previously didn't have perfect pitcu suddenly find they do - or can the perfect pitch lot just adapt? I mean, is the perfect pitch there in their head fixed or is it tunable?