If a unit is already hidden, no matter the unit, it doesn't count towards how many you may hide. So over the course of several turns, a leader could hide their entire force.
This is an act of the "Leader" (in actuality the command and control network) giving orders and locking down communications for units that are concealing themselves.
Aerospace units start as hidden because space is HUGE and we just assume everyone starts the game out of sight of everyone else.
