About assistant professor job postings with no set deadline
One possibility to be aware of is that tenure track hires usually need to made after a national search. Yet some departments like to hire by going after "targets of opportunity". These are individuals already in faculty positions whom the department have identified as exceptionally talented and potentially willing to move. In order to facilitate this process, some departments keep an open search on the books for a protracted period of time. 

The point is that some fraction of these rolling searches are probably not intending to hire from the pool of applications that come in unsolicited. That said, I also know of cases where the applications that come that way turn out be so strong that a department ends up hiring from that pool.