I depends on the particular flights. In some cases there may be as many as 42 J seats unsold with 0 (yes, zero) C seats available. If you want to check yourself, you can see C space numbers at
http://www.flyaow.com/classamex.htm .
<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Is there a move underfoot to regulate upgrade space by playing with the fare class inventory?</font>
This has been suspected since October 1.