For new players - they can run 16 scouting parties from one of their Tribes and sub units of that Tribe in any combination as long as no one unit runs more than 8.
Both units are in the same tribe, neither are sending more than 8 scouting parties, and the total number of scouting parties is less than or equal to 16
All units are in the same tribe, none are sending more than 8 scouting parties, and the total number of scouting parties is less than or equal to 16
One of the units is sending more than 8 scouting parties - not allowed
Two tribes are not allowed to take advantage of this rule at the same time. Only ONE tribe may send 16 scout parties, all other tribes must then restrict themselves to 8 scouting parties