I wonder how one can have no upgradeable C class seats in business class, when 20/25 business class seats (as per the seat selection option) are open.

I am talking about the Toronto to Miami flight on Xmas day -AC 3231 - when the advanced flight option shows that business class has J9C0. The plane is a B767-300 ER.

I would have thought there would have been at least a good half-dozen upgradeable seats, with 20 seats available.