Years ago I had a friend named John B***n. John had perfect pitch and we had long discussions about it. John said he wasn't born with it but he developed it over time as a piano tuner when he was very young; in his teens. He learned it working with tuning forks. He was capable of recognizing tones based on experience. He wasn't hard wired with perfect pitch right from the factory. But once heard he could remember what a sound was like.
Johns full story isn't happy. He was declared as Schizophrenic but I believe that was later changed to autistic. I met him when I worked in a half way house for people with mental disorders. John would listen to a song and as long as I had the lyrics he'd write down the chords. He was never wrong.
I asked him once if the records were ever sharp or flat. He said they always were and he was just cleaning them up for me. He never went to concerts because of the noise. (he said) I lost track of John over the years and would like to reconnect. Not because of the perfect pitch chord thing, but because he was good friend.