Here's the reply I promised. Nothing new or encouraging in my opinion.
Thanks for your email to the Carnegie Mellon University Office of Admission.
We are still currently receiving last minute waiting list reply forms, and we will not know the exact number of spots available for waitlisted students until May 1 when enrollment deposits for accepted students are due. We do not fill any acceptance slots until that date. Therefore, we don't have the records available for the numbers you request. Additionally, we do not rank students on the waiting list. Therefore, you will never be particularly placed ahead or behind of other students. Instead each college will see how many spots are left and the admission counselors will reevaluate each application based on your original application and any additional material we receive. Your best chances for getting off the waitlist is to just submit supplemental material that demonstrates why you are a good match for our university.
As far as acceptance, it does vary from year to year. Last year, we were unable to admit any waitlisted students. However, in the past we have admitted up to fifty students.
Best regards from Carnegie Mellon's Office of Admission.
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