As far as I understood it, Asia Miles is the basic level and by completing a minimum number of sectors or miles your status gets changed to Marco Polo Silver. That's what happened to me after a oneworld Global Explorer J class journey anyway. Last winter I didn't fly the required sectors and was therefore moved down to Marco Polo Green level. In all honesty it doesn't make a huge difference other than no longer receiving the quarterly magazine. All I'm interested in is getting redemption tkts rather than other privileges.