Between the two classes, a couple people got quarantined and pushed back slightly, shortly before evals, due to a covid exposure. Their spots stayed on the lists. Also, if anyone chooses ZUA, ZAN, or HCF, then their national spot stays on the list.
There have been classes, months ago, that had to start over completely due to covid, regardless of vaccination status. Now, if you're vaccinated, you're fine. If you're not vaccinated, then you have to quarantine and they will try to fit you in with a class not too far behind you.