You want a REAL headache due to a time travel story? Try TAS's "Yesteryear".
Using the Guardian to view the past, in particular moments during which an adult Spock saved his younger self from death, caused the older Spock's presence in the past to be erased, thus cluing them into the fact he had to go back in time in the first place.
Huh?
You have it slightly mixed up. The way adult Spock remembers the events:
- shortly before the official Kahs-wan rite, nearly-7-year-old Spock decided to do a trial run, to prove to himself that he could manage the official rite, so as not to embarrass his father.
- around this time, an older kinsman named Selik was visiting the family.
- Selik saved Spock from the wild animal.
- Selik left shortly after (next day?) and was never seen again.
- 7-year-old Spock passed his Kahs-wan with flying colors.
How this got mucked up on the Guardian Planet is that a group of historians were researching some event in Vulcan history that took place at the same time as child-Spock's decision to undergo his trial run at the Kahs-wan. Because adult Spock/Selik was not there to save child-Spock, child-Spock was killed by the wild animal. Therefore, adult Spock never existed and the other crew didn't remember him (naturally). So adult Spock realized that
he was actually Selik, and he went back to fix the timeline.
Makes sense so far, except...
...the next time anybody researches that particular time in Vulcan history and adult Spock isn't there, will child-Spock be killed and adult Spock will have to fix things
again?!
In "Tomorrow Is Yesterday" they had to find some way to keep Captain Christopher alive long enough to father Colonel Shaun Jeffrey Christopher. As for the security guy, that was a funny subplot and at least he got some chicken soup out of the deal!
It's worth tracking down Mark Andrew Golding's essays regarding time travel and alternate universes in various volumes of
Best of Trek. They're well-written, if mathematically headache-inducing, and he goes into detail about why the events of "The Naked Time" doesn't result in new Enterprises being created out of nothing every 3 days.
What gets me about Trek and time travel is why Kirk wasn't worried about Gillian Taylor changing history if she were left on Earth. He didn't want to bring her along to the future, which is a contradiction to previous ways he had of looking at this sort of thing.