In 2269, information about Zor Kahn was stored in history tapes on file at the library which was then under the care of Mr. Atoz. Spock briefly viewed a history tape mentioning Zor Kahn before discussing with Mr. Atoz the workings of the Atavachron. (TOS: "All Our Yesterdays")
Little is spoken of Zor Kahn in "All Our Yesterdays" except the brief mention that Zarabeth shares with Spock. It is also unknown when exactly Zor Kahn ruled on Sarpeidon or how long ago he had banished Zarabeth from the time the Enterprise landing party arrived on the planet (given the nature of time travel, this could have been anywhere from a few days, weeks, or even centuries). In the episode's script, Spock tells Zarabeth that Zor Khan has been "deposed and executed more than a hundred years before we arrived at the library", but this line was cut from the episode itself.