My guess is that before 2008, Singapore used basically reprinted versions of the HK stuff. Mainland chinese releases did the same thing (Mainland chinese releases had both the AVTCD stock number AND the SCD stock number on the packaging). Probably after that, singapore & malaysia got a specific pressing (and therefore new stock number) for that area. My guess is that it stands for something like Avex Asia J-Pop CD.
EDIT: I just did some surfing and it seems that AAJCD is an alternate HK stock number prefix.... ayu's avex asia discography has both stock number prefixes. AAJCD and AAJSG seems to have come into play from "GUILTY" onwards. (
http://www.avexasia.com/cn/artist/ar...HAMASJ&t=1&s=2)
Can anyone with an HK version of GUILTY or A COMPLETE comment on that?