It isnt up to me as the event organizer. i turn in my scores and they decide. but im pretty sure if you have attended other events and already scored points this season you have a higher chance of going to nationals even if you place lower in a single event.
They also only do so many NYYL events each year so only so many events people can score points at. i would say its safe to assume the top few but i dont give you a specific # like top 5 will make it because i dont make that call.