There were a few data signals going into Friday’s blockbuster jobs report that many market watchers and economists missed. Layoffs, as measured by a rolling four-week average of initial jobless claims, hit their lowest level in more than a year and a half. August showed an uptick in job openings, a hint that companies were about to ramp up hiring. And September’s ADP National Employment Report suggested that a rebound in private-sector hiring was under way.