It is a formula, no committee decisions.
1 Top 2 in each of the 9 Regions are Automatic
2. of the 'third' place teams which one beat the most of those 18 teams [beating a team that was not running a full team does not count - Wisconsin at Nutty does not count because they only ran 3, not 4 or more of those that run Regionals but since two top guys were sick, maybe an added runner made them an 'official' team.
3. The number 4 team in the Region at added the first #3 now is effectively a #3 team. Of all the #3 teams which one has the most points gets in (note that the added team gets counted among those that can add a point). Continue this process until you get the full field EXCEPT for PUSHES
4 A team with a lot of points but not a "#3" team can push another team in but the pushes are not certain until later because it does not count as a push if that pushed team gets in on its own, which is determined by going through the rest of the potential teams to add. This is the tricky part but is also definitive; there is no uncertainty getting in.
Notes, ties are broken by a sequence of, I think, 1) head-to-head result, if none then, 2) common opponents, and 3) something else I do not remember). Some posters must have posted this elsewhere because there a several 'mavens' out there that know all the details and that can parse them correctly to get it determined. The NCAA does not announce until the next day to check. It gets a bit tricky to check all of those teams that are beaten to provide points to determine if they count as a team (see 2 above). Someone stated about beating teams that are not in the already-qualified list and that is probably a typo since that is a senseless criteria [e.g., get in by going to a lot of races with many bad teams to wrack them up...]