I think most R1 schools will have a historical average yield rate around 50% (the amount of extended admission offers accepted). So if you interview with a cohort of 20 and you later find out they have 10 real spots, then you would all stand a good chance of getting an admission offer. Those offers might not all go out at once if they don't want to overshoot the number of open spots they have, and in that case they will make use of a waitlist while they see if their top 10 choices accept or not.