Just because it’s on Quora, or CC for that matter, does not make it accurate. Harvard sends out roughly 300 likely letters. That is accurate. But it is for the whole admissions cycle, not starting mid-Feb, but October 1. But ~200 go out in Fall to recruited athletes, with the balance going out in Spring to non-athletes. 300 ‘Likely Letters’ Sent to Class of 2015 | News | The Harvard Crimson.
Early writes are done for recruited athletes, generally the summer after junior year, and are based on GPA and test scores. I don’t know what they did this year with test optional.
Early writes give the athlete some direction as to what the admissions decision may be, but it is not a guarantee. Likely Letters require a completed application.