Chicago seems to send a slew of rejections on one day in late Feb/early March and a series of MAPSS/CIR letters/PhD rejections the next day. I asked about acceptances and she responded that "answers" were still to be revealed this week/next. Perhaps it's wishful thinking or projection, but that didn't read straight up rejections to me. I guess it means that they're breaking from their normal routine regardless and we're just left to wonder whether that means spacing out acceptances and waitlists or throwing up rejections a couple weeks early.
Edit: Having a think about it, the actual question I asked was whether all of the acceptances had gone out yet, and her answer was no, with the additional information following. So I'd say that the pattern shift is toward the acceptance/wait list spread.