This was originally supposed to be the third season finale. There were some minor rewrites, with many of Kes's lines given to Seven of Nine.
In one scene, Seven of Nine tells Harry Kim and B'Elanna Torres of the Borg being present when Zefram Cochrane launched his first warp-driven starship. She claims it is "complicated" when they ask her to elaborate. This is an acknowledgment of the events of Star Trek: First Contact (1996), in which the Borg travel through time to assimilate humans and remove their resistance.
Before and After (1997), in which Kes travels through time, gave a preview of this show by showing a time-line in which Voyager had already been through the "Year of Hell."
Captain Kathryn Janeway's birthday is May 20th.
The Astrometrics lab is unveiled in this episode.