Am waitlisting on an award Y tic TPE-HKG so checking the inventory quite frequently.

On expertflyer, it's showing Y9 B9 H0 K0 M0 L0 V0 S0 N9 Q0 O0
However, when I called MPC, the lady told me that the flight is flatly overbooked in Y.

What does N9 mean then? I thought it's a discounted Y class but then how come all the other discounted class tics are gone but N class still showing 9?