This is the line to look at for 2.4 GHz -
managed, AP, mesh point, P2P-client, P2P-GO } <= 4
So if you have any AP's or mesh points, they count against the 4.
Yep, 16 is the correct number for 5 GHz -
managed, AP, mesh point, P2P-client, P2P-GO } <= 16