Question about Hextech Boxes and premades

It says that if anyone in your premade group gets an S, it counts for the whole team.

Scenario 1: Two people get S's. Does that count for 2 chests? Or is it one per game?

Scenario 2: A friend gets an S with Olaf this game. I get an S with Olaf next game. Do I get a box the next game or did his S count for my champion too?

Scenario 3: I already unlocked 4 boxes, but get an S with a 5th champion (Zyra). Can I still unlock a box the next month with that champion (Zyra)?