There are always exceptions to any rule. The duty manager can give an op-up as they please, regardless of fare class and/or member status. But more often, the general rule is higher paying fare (Y,B,M) customers are given first consideration regardless of member status. This information comes from OZ management.
I tested this over multiple years during peak summer travel between Korea and the US when economy cabin is usually oversold. Tickets with fare code Q,K,S,V,W,T..... don't count on getting an op-up. But when I've purchased full fare Y or B fare codes.... boom automatic upgrade at check in or at the gate. Is it possible a Plat with lower fare codes such as V, W, or T can get upgraded? Sure. But will it happen every time? In your case, it may be possible they already upgraded Y,B,M full fare customers, if there were any that paid for such fare.