Yes the will have seats left by then. Schools ensure seats are left even for late interviewees, that is why the people interviewed earlier end up on waitlist. If they didn't do that, spots will be gone before others had a chance.
here are stats for fall 2001 admission from USnews.
applied : total - 7387 instate - 868 outofstate - 6519
interview: total - 1627 instate - 380 outofstate - 1247
accep: total - 861 instate - 261 outofstate - 600
enrolled: total - 237 instate - 80 outofstate - 157
hope that helps.
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