Can you guess this note? Perfect Pitch and Physics

Perfect pitch can also be lost. I started playing the piano at age 6. It took a music teacher who was teaching me clarinet at age 12 to notice - in theory tests - that he could play any note on the piano and I could name it instantly. No-one else in the class could, and I became a bit of a celebrity in the school for it. Stories like "she can even tell you the note of the aircraft flying overhead" (not really true...) spread. I always found it tougher with  instruments other than the piano, but could usually manage it. With voice, I could usually get it right, or at least very close.
But now, it's gone. Not completely; sometimes I will absolutely know that note you played on the piano is a C, or whatever. But very often I will be quite unsure. And it's not even a proximity thing; sometimes I might be unsure if a note is (for example) a Bb or an Eb, but I think it is one of them.
Maybe it's a result of not being tested, and not testing myself on it. Maybe it's because I played a piano that was out of tune for a while (that is, incidentally, very difficult if you have perfect pitch, because you keep thinking you're playing wrong notes). Perhaps I should try to train myself again and see if it comes back.
I never developed relative pitch properly. In my music theory exams, they'd play an interval and ask me what it was. I'd say "a D and a G, therefore it's a perfect fourth". So I had no need (from an examination point of view) to develop that skill.