The business seats got snagged by coach pax who were upgraded because of the oversell (probably elite customers, full fare, etc). The cleared list you were seeing didn't show as a standby list, because those were revenue pax without a seat (shows up as HK on travelnet and they have basically #1 priority for seats).
Your plan to get business works well if coach has no-shows and isn't actually oversold... otherwise you'll get left behind.