If you search back in this thread, they often do not reply to updates- I think they had said they had more applicants this year than ever before- I want to say upwards of 8,000+. You can call and they will confirm that it has/has not been added to your application. People also email directly to the Dean of Admissions, but this is typically post-interview. I know that when I sent in an update letter about a week before my interview, they did receive it and my interviewers had it on hand during the interview day. Be sure to include all the pertinent info they would need to match your letters up with your application- most importantly your AMCAS id# in the subject line and in the body of email/ letter as well as your interview date (if applicable). Hope this helps, don’t be afraid to call and confirm!