Out of curiosity, did it shift up or down for you? I've had perfect putch from a young age, but now at 30 I hear everything a semiton higher (so e.g. a B sounds like a C to me, and I have to manually subtract the semitone to infer the real pitch and hope that I am not overcorrecting)
Pitch perception shifts with age?
It's well known people with perfect pitch always lose it in middle age, the reason is unknown, but it's always extremely upsetting when it happens, and since perfect pitch isn't very useful to begin with, it's actually a curse.
Does that imply that people with age actually interpret pitches differently? The pitch reading would be correct "locally", within your brain.