I did some digging through the Mizzou and the waitlisted threads from last year, and it looks like last year
-Very few people were taken off the waitlist (lots more initial acceptances than they expected, so almost no waitlist movement)
-Nobody was notified about movement off the waitlist until right after the April acceptance deadline, meaning if you had an offer elsewhere you needed to accept it and then back out if you managed to get off the Mizzou waitlist & wanted to go there instead
-They didn't give numerical rankings if you emailed, though they would say things like "you have a reasonable chance" or "we only expect to pull 1-2 at this point, we're sorry" that could give a subjective idea of where you might be
I don't know how much of that applies/will apply to this year as well, but like :/