I called AC reservations about AC 3231 on Xmas day. They stated that the economy class was oversold (not suggested by the seat selection option - many seats are available for purchase), and 8 seats were blocked for possible operational upgrade because of the oversold economy seats (again, the seat selection option shows 20 business class seats are open, and only 5 seats are purchased).

Can anyone explain the discrepancy with what the AC reservations agent told me, and what the seat selection option shows in the figure, in terms of available economy class, and business class seats?