The fourth example depends on the difference between what the speaker knows and what the listener knows.
Situation 1: The speaker knows Zayd has not arrived; the listener does not, and there is no counter-indication. The predication can be assessed in its ordinary apparent form.
Situation 2: Both know Zayd has not arrived. The shared knowledge invites an inquiry whether the utterance serves irony, humor, or another purpose.
The reality/belief grid is therefore a necessary analytical aid, but it cannot replace close attention to the listener and contextual signs.