You could easily be looking at the difference between unbooked, and unassigned. I would say there is 3 seats left...the other two are booked but not assigned.

Seating charts available to the public are notoriously unreliable. Another source would be the fares still available. Do you see A3 (or A5), Z3 (or 5) P3 (or 5) so on for the various fares you need to know about.