And then somebody would need to lose that research between 1962 and "today" (2260-whatever). It's not as if Kirk and pals could add anything of note to whatever the contemporaries already wrote about 1962, considering they are dilettantes when it comes to history, and are just visiting anyway, unable to grab or comprehend any context.
And of course absolutely everything that happened made it into the history books. Not one scrap was left out.
Nope, that's not how it works. There are lots of things you're not going to find on Wikipedia (or the Federation equivalent), because the hard records were lost or destroyed before they could be digitized, or even the digitized records were destroyed. There are some things that happen that never do get recorded. That's why archaeologists and historical researchers aren't out of work. There's still a hell of a lot to discover.
It's obvious that Gary Seven's presence in the late 1960s never made it into the history books, or Kirk and Spock would have already known about him.
So, did Earth lose its history in a post-20th-century disaster? As per "Space Seed", interplanetary shipping records were a bit jumbled for 1996, but whether due to later loss or contemporary laxness in wartime bookkeeping, we don't know.
It's not that hard to lose history. Not long before the 2015 federal election, the federal government here in Canada (when Stephen Harper was Prime MInister) decided to literally trash and burn entire environmental science libraries. They burned records going back decades, since that information would have helped the environmentalists fighting the oil and gas companies. They swore up, down, and sideways that they digitized the information before trashing the physical records... and if that's true, I've got ocean front property outside my front window for sale (I live in a landlocked province in Canada).
Star Trek's in-universe history includes more destructive wars than we've had so far (thank goodness nothing like the Eugenics wars or WWIII has happened... yet). So there are more opportunities and reasons for certain historical details to get lost or deliberately forgotten.
When in doubt, "subspace". Sol could be different in many ways, some of them responsible for the fact that slingshotting only ever happens around Sol, others for the fact that heroes and villains in extreme hurry sometimes drop out of warp at Sol and proceed at impulse, even when everybody from Cochrane and Archer on jumps straight to warp from Earth orbit at other times without any particular hurry in evidence.
...
And nobody in Trek does. But tellingly, nobody in Trek does it around nice and dull K stars, either. Except for Sol.
Or maybe it's just a coincidence that nobody's had a reason to do it except around the Sun. It's a difficult and dangerous procedure, and not something to be done casually.
Sometimes our heroes or their bosses balk at altered history. But generally, they can't tell the difference (nobody we know ever failed to have that bum vaporized, say). It's a bit difficult to see what sort of a "blunder" or "alteration" would make Starfleet distrust time travel, then. (Or Klingons or Romulans, who must have spies everywhere and be aware of slingshotting. Although if it can only be done around Sol, then they're screwed.)
I just mentioned an essay that speculated that the bum's death is why there's no TV show called "Star Trek" in TOS' in-universe history. The essay speculated that the bum's disappearance led to his eldest son (hypothetical that he had kids) turning to a life of crime to support the rest of the family, which in turn led to an encounter many years later with Roddenberry before he became a writer... an encounter Roddenberry didn't survive. So if Roddenberry died before creating Star Trek, that's why there's no "Star Trek" in Star Trek.
Yes. So we're to believe that between 1960 and TOS, humans just stopped bothering to keep records. And then Starfleet decided that the best use of resources is to just time travel and have a look around. Sounds fair.
As I've said, sometimes records get lost. Sometimes they get deliberately destroyed. Did you record absolutely everything about your own life? Do you even remember absolutely everything about your own life? If you were to look up a history of your own city, would you find everything there that you remember personally? I doubt that.
My feeling is that the Aegis (the organisation which Gary Seven worked for) reached out to Starfleet and asked them to send the Enterprise back in time, as they knew from their own records about Kirk's involvement in those proceedings.
Starfleet didn't know the full details, but knew enough to know that when the Aegis advise a course of action, it is best to follow it!
So, off goes the Enterprise to 1968
Starfleet didn't know about Gary 7.
I guess you could extrapolate and stretch continuity a bit and say the Department of Temporal Investigations set it in motion, since they
would known by their century.
I always wanted to see more of Gary Seven and Roberta Lincoln's adventures. I am quite content to include John Byrne's "Assignment: Earth" comics in my head canon.
Kor
I wonder if Teri Garr would have wanted to do a series. I read in an interview she gave that she hates being reminded of Star Trek, and her comments about it included, "Don't talk to me about Star Trek fans. Those are the kind of people you see at swap meets!" (paraphrased).
So her nose has definitely been in the air for a long time. Those comments have somewhat tainted my subsequent enjoyment of this episode and any novels that mention Roberta Lincoln.
I still think somebody should reboot "Assignment: Earth." You wouldn't even need to maintain a connection to STAR TREK. Just call it "Gene Roddenberry's ASSIGNMENT: EARTH."
Yes, it could make an interesting series, and go in a variety of directions.