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...
Historically, as I recall, A was a bit lower than 440 as testified by older wind instruments and organ pipes.
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1. Granted, the player’s technique also affects intonation so this is not insurmountable.