Okay, so every month all the interviewed candidates are ranked on a list, with a numerical point value down to something ridiculous like 4 decimals. At the end of every month the top 5 or so are taken from the list and given acceptances. March is the final month for regular (non-waitlist) acceptances and so they'll start pulling from the top of their list until they reach the class size of 96 (or possible 104, depending on funding status of the year), with another 96 or 104 on the waitlist. As people withdraw for whatever reasons, more and more individuals are pulled from the waitlist and given acceptances, including those who do not make the original 96 cutoff. As far as I'm concerned, no one is ever rejected until March 15.
tl;dr it is possible to be accepted at any time.