The ambient noise level aboard the ship was increased in the alternate time-line. Consoles and displays were made more audible, the warp engines made a dull roar sound, intra-ship communication announcements increased, the doors made a "swoosh" sound reminiscent of the sound effect used in the original Star Trek (1966) series. Set lighting was also significantly changed and darkened.
In the alternate time-line, this episode's story writer Trent Christopher Ganino's name can be seen on a tactical situation monitor showing the progress of the Klingons in their war with the Federation.
The trivia items below may give away important plot points.
In an early development for the story, Ambassador Sarek (Spock's father played by Mark Lenard) used the Guardian of Forever (Star Trek: The City on the Edge of Forever (1967)) to replace Surak, the father of the Vulcan philosophy of logic who had been killed resulting in a new time-line rather than Tasha Yar performing a similar service.