Notes in AY music

Hello, All Such a question. I was selecting all sorts of AY melodies on synth and came across this phenomenon - the real sound almost everywhere differs by several notes from what is written in patterns. Within one “batch” this displacement is the same, but in one module may be different. I heard there were some special features with division setting frequency inside AYka, but then certain notes would simply sound wrong, but here they sound correct, but shifted. What is all this about?