Quoted from jrcw:Sounds are on different rom chips than the code itself so I think they are released separately.
Quoted from AlexSMendes:So you're saying that you have a sound rom version that no one else does?
He's running a special software version that was made for IFPA (I have a TZ version for IFPA as well..), and the game currently has P-1 Audio ROMs installed. So, yeah, if the serial number didn't give it away that game's at least an early one.