The Pittsburgh Steelers have hosted 4 players on official pre-draft visits so far this offseason. Each team is permitted 30 official visits with prospective players, but in some circumstances visits don’t count.
For example, although the Steelers have hosted 4 players, if some of those prospects went to school, or where they grew up they wouldn’t count towards their overall total.
As pointed out by PennLive.com’s Jacob Klinger, in 2017 before the NFL Draft when Michigan State safety Montae Nicholson visited the Steelers, the visit did not count against the Steelers’ 30 due to the fact he grew up near Pittsburgh, Monroeville to be exact.
The official verbiage the NFL uses is “exceptions for players who attend nearby colleges or grew up within the same metropolitan area or the "contiguous suburbs."
Also per Klinger:
Each NFL team is designated three local Football Bowl Subdivision schools, including at least one in a Power Five conference whose players they can administer medical examinations to without counting against the 30 pre-Draft visits. There are also rules preventing teams from evaluating players physical (ie. testing, timing) if they provide transportation to the player, regardless of where they're from or went to school.
Players from colleges within a 50-mile radius of team headquarters also don't count against a given club's 30-player limit.
Therefore, there is a good chance the Steelers will get more than 30 visits this offseason, based on the products from the University of Pittsburgh, as well as those who have grown up in the metropolitan Pittsburgh area.