That may only refer to credit units toward the number needed to graduate. Subject credit and advanced placement may be a different story. Credit units without subject credit or advanced placement may only be helpful if the student completes all subject requirements to graduate, but is otherwise a few credit units short of graduating early or avoiding graduating late.
Regarding MIT, https://firstyear.mit.edu/academics-exploration/ap-and-transfer-credit/advanced-placement says that “A score of 5 on both of the Capstone exams - AP Seminar and AP Research, earns a total of 9 units of unrestricted elective credit.” (Note: 9 MIT units appears to be equal to 3 semester hour credit units at universities where 120 semester hour credit units are needed for graduation.)