<p>I know this from several sources. First from books by authors who had access to the inner workings of admissions committees at selective schools, such as The Gatekeepers by Jacques Steinberg. I recommend you read this book if you haven't. It's an eye-opener. Also last year I personally had an extended discussion with an adcom from MIT. I asked her directly, and she confirmed that it is true. The committees really do continue with the horse trading right up to the end. She told me that it was worthwhile to notify the schools of any late-breaking SIGNIFICANT honors or achievements that might tip the balance in favor of the applicant. They might be one of the ones on the bubble.</p>
<p>As for early or late in the process, everyone gets a read through and evaluation before any decisions are made. Some of those are clear admits or clear rejects, and they fall in or out early and stay there. No additional evaluation is needed to confirm their status. It's the near the borderline where all this late activity occurs.</p>