I suspect that the Harvard acceptances might not yet have been notified, whereas waitlisted have, only because waitlists are the department's own shortlists, but acceptances must be approved by the Graduate School, and so maybe, especially since admissions are uncertain this year, the department/POIs are holding out until final approval by the Graduate School before notifying their accepted students. On the one hand, hard to believe that no acceptances would post in the Results, but then again, only a small fraction of total applicants post results anyway, so the 6 people, as you say, could simply not be on GradCafe.