I JUST asked one of the PCOM adcom members who visited my campus today, and asked if they were still reviewing in order of primary application submission. She gave me a "yes, kinda" answer. Apparently they have batches of apps they look at together, and specific committee members go over applicants who have certain similarities, e.g. they have a DO letter (not a requirement), or they're from a certain program, or they're in state, or did this extracurricular, etc. It almost sounded like it was the choice of the member to choose what criteria to look at? But all people in that batch get looked at the same time or thereabouts for interview selection.