The "month" is really an estimate-there are some faculty members who go a little M.I.A. for a bit, so I would give it until 6 weeks? Definitely go through your spam though like
@Doctor Strange said (I know that's not what you want to hear but there's a good chunk of people whose email realizes it's bad news and buries it)
Committee weighs the student and faculty interviewer, and make a decision. "Final say" doesn't really exist, although Callahan definitely weighs a lot in case of uncertainty. I would also believe Callahan determines who comes off the waitlist when that time comes, but there it committee involvement in that too (I think, that part I'm not 100% sure on)
Also, I said this what feels like last week, but just because they didn't take your update letter and immediately give you an II doesn't mean they didn't get it. It doesn't mean they received it and tossed it out. Those cases are possibilities (n=1 ALWAYS), or it means that they either haven't gotten to it or got to it and decided to wait on it for a little while. Check my old post about this a couple of pages back on update letters, but just a reminder that if you send them an update letter that doesn't actually update them on anything, they aren't going to be receptive to it and it's honestly kind of a rude waste of the office's time. Jefferson is very receptive to letters, but make sure they actually have something relevant in them, and aren't just "I heard on SDN if you send letters you get an II"