In 2267, Bates and Lieutenant Dave Galloway were ordered to accompany Captain James T. Kirk and Commander Spock to the surface to the planet Gateway to locate Dr. Leonard McCoy. (TOS novel: The Fire and the Rose)
In 2269, Bates again accompanied Captain Kirk and a group of historians to the surface of Gateway to perform historical research using the Guardian of Forever. Because he was a member of the original landing party that discovered the Guardian, he had clearence to accompany Captain Kirk and Spock into Orion's past.
When the landing party returned to the present they discovered that history had been changed, Bates and the others returned to the ship to ascertain what had transpired. On the order of Enterprise first officer, Commander Thelin, Bates performed a record search to any references to Spock or members of his family. It was then that the team discovered that history had been changed when Spock died in 2237. (TAS episode: "Yesteryear"; TOS novel: The Fire and the Rose)