When Koenig and Alan are crash landing, close-up shots of Koenig (as well as SFX shots of the crash) were re-used from Devil's Planet (1977). Since Koenig was in the pilot's chair previously and is in the co-pilot's chair here, the picture is reversed (at 18:29, the number on the cockpit door is backward).
According to Helena's status reports, The Lambda Factor (1976), Devil's Planet (1977), and The Immunity Syndrome (1977) all occurred within a week (2308, 2306, and 2310 days after leaving Earth's orbit, respectively). In fact, the planets featured on the latter two must have been impossibly close to one another, as they took place four days apart (with "The Lambda Factor" right in between, which showed no planets in close proximity to the moon).
Martin Landau and guest star Karl Held previously appeared together in The Outer Limits (1963) episode The Man Who Was Never Born (1963). Held and Alibe Parsons both appeared in the Joan Collins film The Bitch (1979).
Guest star Karl Held (who played Lindstrom on "Return of the Archons" (though credited as Christopher Held) joins Joan Collins as the only actors to appear on both this series and Star Trek (1966).
The script this episode was based on (but heavily re-written by Fred Freiberger) a Johnny Byrne script employing the Season One format and titled "The Face of Eden" (a story told in flashback format involving Koenig, not Tony, going mad with the survey team trying to get him to remember what happened to him). Byrne received sole writing credit for the filmed episode, but it only vaguely resembles his original script. Freiberger gave it the title of a Star Trek (1966) episode for some reason.