yes- everyone and every school is different. Mich and Pitt had auto invites for some candidates. i.e. instant interview invites even before secondaries in some cases. others schools (for the same candidates) may still not have said anything months and months later (hold, reject, interview, etc). Stay patient, send updates, letters of interest.
From years past, I've heard of schools never getting back to a person regarding their status past the 'complete' stage.