Not entirely sure what you're asking. But I'll give it a shot. If there are three sessions, each with a potential 333 people signed up for each of them, you'd only build 3 sessions. I'm not sure what the other alternative would be.
Example: I have as many as 5000 users at any given time (far more accounts at this point) and a few hundred classroom events (topics) going on each year. Those users are eligible (mandated!) to attend specific topics in specific locations. Each topic has a F2F section with all the available sessions people can sign up for...If we teach Sexual Harassment (don't do it) 10 times, and there are 250 staff who can sign up for the class, I create one activity with 10 sessions, each, in theory, accommodating 25 people. It is rarely that clean but that's sort of how it works.
I've been told it is possible to csv sessions but it would be extremely time consuming and potentially dangerous. I wouldn't.