I checked for an article from the Harvard Crimson about the degree to which the admission office follows up on admitted students after they enroll, although I didn't find the link just now. You've received other replies mentioning various ways, with various degrees of formality, that admission offices can and do check their results. Now that many admission offices are making very fine distinctions among applicants as admission rates plummet below 10 percent, there will probably be growing interest in validating the criteria on which admission decisions are made.
MIT admission office McGreggor Crowley, in one of his admission travel sessions in the last year, said his office has done studies of which students perform best in upper division courses at MIT. Taking really hard classes in high school is a better predictor of upper-division success at MIT than having a spotless G.P.A., for example. He asked a large audience of high school students how many had done baby-sitting, and very few raised their hands. He said if that is one thing that kept you busy in high school, be sure to mention that on your MIT application.