Commander Thelin's collar is black but is blue in some shots during the meeting in the briefing room.
There are a number of mistakes concerning the Guardian Of Forever. In The City on the Edge of Forever (1967) it was surrounded closely by ruins. In this cartoon it is shown in a clearing with only remnants of them. The voice was originally quite deep, and slightly enhanced electronically. The entire "ring" flashed in synchronization with its speech. Here the voice is much higher pitched; sounding old and weak. There is no flashing during its dialogue. Additionally, it now has the ability to "prepare" a time and place to receive the time traveler where as it originally could only show the past like an extremely sped up film. Reaching the exact time and place desired required careful calculations with no guarantee of complete success.
Commander Thelin, an Andorian, is colored with a gray complexion. In all other productions, ordinary Andorians have a vivid blue complexion. The psychic, blind Andorians (Aenar) have gray skin.
If Spock died as a child in the altered time line, then he as an adult should have been erased. He shouldn't be alive to go back and fix the time line; but then, in The City on the Edge of Forever when McCoy passed through the time portal and changed history, Kirk, Spock and Scott should have vanished along with the Enterprise, but didn't, demanding more of an explanation beyond surface evidence (that's never given).
When Spock's clothing bag is beamed down, the wrong sound effect is used. it is the Guardian's sound when Kirk and the archaeologists returned at the beginning of the story.
When Kirk, Spock, and Lt. Erickson return from observing Orion's past, the crew does not remember Spock. Only these three do; however, Kirk says several times that he's the only one to remember Spock. He neglects to mention that Erickson does too. (Erickson was in the briefing room researching why Spock's existence has been altered.)