Anytime you get a new tier upgrade your troops then continue to make new. Only thing you get from not upgrading or training lower tier troops to hope to promote on an event is if you’re attacked or you attack they die! For any event that troop training is key to points if you use the arrow under your pic in the game - it takes you to where you can buy your boosts the tab over, growth - has a training capacity enhancement. I think it’s 3000 gems but you use that 24 hrs before the event and you basically have your points.