Try to look at the seat map it will tell more at least in Business and First that most have preassign seats, but even that some time not correct.
I did check the seat map as well. When I checked in online 9.5 hr before departure the number of seats already assigned were: F 5/16, C 31/66, Y 208/260. I don't know what F was like in the end, but C was full (at least up to row 15) and presumably so was Y.
I suspect many of the C seats were eventually occupied by SWUs and op-ups like myself.