On domestic and transborder flights, the availability display is extremely misleading. AC will often shift J capacity into Y to sell more seats because the chances of a domestic or transborder flight selling out in J is extremely small. So even if you see economy booking classes showing as 9s, that doesn't mean the flight is not oversold. On the other hand, if you see things such as J5C0 on an international flight, chances are that there really are only 5 J left. Yield management does not care how many status members are booked in Y (i.e. they do not hold seats back just to make sure status pax will get their upgrades).