No one outside of admissions would know that one. But UMich does accept about the other half of acceptances (7,500-ish) in RD. % would depend on the amount of total apps.
Also, there are sometimes “here and there” releases of RD decisions in between the bigger “waves” on or about 2/1, 3/1 and 4/1. Also, FYI, there have been waitlisted applicants that have heard as late as June and July.
And postponed = deferred.