According to Wikipedia (https://en.m.wikipedia.org/wiki/Alien_Nation) the original movie released in 1988 was adapted into a TV show. The series ran for 1 season of 21 episodes but was then cancelled. The network continued the story with 5 TV movies (Dark Horizon, Body and Soul, Millennium, The Enemy Within, The Udara Legacy).

Because of this I think those 4 should be a collection but the original 1988 release should be left as a standalone film.