I don't have perfect pitch, but I basically have a 440Hz sine embedded in my brain which I can use for tuning stuff and figure out the rest through relative pitch. Perfect pitch sounds actually extremely distracting as a listener...
It’s very much a regional thing where Europeans tend to tune higher than Americans, as I recall. A lot is going to be dictated by the pitch of the local church organ.
Historically, as I recall, A was a bit lower than 440 as testified by older wind instruments and organ pipes.
A440 was standardized in 1939. There was an earlier attempt to standardize on A435 in the late 1800s, but they specified a temperature uncomfortably cold, when you move something (I'm not sure what) tuned at A435 to a more comfortable room temperature you get close to A440, and from there a little rounding and we have A440. Before the 1850s every town had their own standard which was mostly based on whatever the A note of their organ was. Turning a pipe organ takes an expert hours and costs a lot of money so if it is in tune without you make everyone else tune their instrument to the organ. The tuning fork was invented in 1711, before then we didn't even have a way to move a tuning between downs - the act of transporting most instrument changes the tuning.
There’s also a standard of using the metric system, but there are still plenty of backwards places that don‘t follow it. One of the instruments I play is flute and while there is some flexibility possible to adjust the pitch by moving the headjoint in or out, there is an idealized pitch for the best intonation.¹ Most student instruments are A440 but some intermediate and professional models are tuned to A442 or A444.
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1. Granted, the player’s technique also affects intonation so this is not insurmountable.
