The canon of Star Trek has existed in a constant state of flux since the beginning of the franchise, and characters like Dr. Leonard McCoy's daughter have gotten lost in the shuffle. The USS Enterprise's resident physician was known for his folksy, old country doctor routine, but much of his personal life was left off the table. Even as he continued on through the feature films, McCoy's life outside Starfleet remained largely a mystery as opposed to those of his companions like James Kirk and Spock. The existence of any McCoy rarely came into play, and he kept his work and personal life separate.
Excluding a few one-off lines about his family in episodes of Star Trek: The Original Series, the only other McCoy seen on screen came when Spock's Vulcan brother Sybok forced the doctor to relive his father's traumatic death in 1989's Star Trek V: The Final Frontier. While characters like Kirk, Sulu, and even Spock had encounters with their relatives on screen, McCoy did not. Despite that, McCoy did have a daughter according to some Star Trek sources, though she never did appear in an episode of The Original Series or any of the feature films.
