A different take on this:
In the TOS timeline space travel technology advanced faster than the TNG timeline. So in 1960's TOS had orbital nuclear weapons, first manned moon mission. By the 1990's they were already exploring and colonizing nearby star systems with atomic powered DY-series sleeper ships. Colonies are already in place in Alpha Centuri and the system that has the planet Canopius (at the very minimum). Aliens like the Vulcans, etc are already encountered. By 2018, faster propulsion (impulse power, IMHO) becomes available eliminating the need for sleeper ships.
One of these newer and faster ships, the SS Valiant, travels to the galactic edge and is swept up in a magnetic storm and carried half a light year past the barrier. Since we know that the ESP abilities manifest in days then in order to get back past the barrier from a distance of 0.5 light year in a short enough period of time before the ESPer was unstoppable by ship self-destruct the Valiant would have had to travel at FTL speeds (like 100c to cross .5LY in 3 days). We also know from "Mirror, Mirror" that "magnetic storms" are the same as "ion storms" and in "Court Martial" you can fly through an ion storm with warp drive so if the Valiant had warp drive then that would have been the go-to to get out of the storm instead of the weaker impulse engines of the day. That leaves just impulse engines or an unknown other type of FTL drive that isn't warp drive for FTL travel for the Valiant.
Sometime after SS Valiant goes exploring, Zefram Cochrane discovers the "space warp" in the Alpha Centuri system. The technology spreads across the "known galaxy".
In the TNG timeline space technology development is significantly slowed. There are no colonies offworld and other races already have space warp technology. Zefram Cochrane builds Earth's first warp drive in 2064? and the Vulcans make first contact. Most of the TOS episodes happen differently and at a much later date. There is no SS Valiant lost at the galactic barrier.
YMMV![]()
There is one big problem with:
By the 1990's they were already exploring and colonizing nearby star systems with atomic powered DY-series sleeper ships. Colonies are already in place in Alpha Centuri and the system that has the planet Canopius (at the very minimum).
Kirk & Spock:
KIRK: Kirk out. Seventy two alive. A group of people dating back to the 1990s. A discovery of some importance, Mister Spock. There are a great many unanswered questions about those years.
SPOCK: A strange, violent period in your history. I find no record what so ever of an SS Botany Bay. Captain, the DY-100 class vessel was designed for interplanetary travel only. With simple nuclear-powered engines, star travel was considered impractical at that time. It was ten thousand to one against their making it to another star system. And why no record of the trip?
DY-100 class ships like the Botany Bay were not designed for interstellar travel. Possibly DY-200 or DY-300 class vessels were designed for interstellar travel and were already in use by the 1990s.
But when Kirk thinks the Botany Bay could be a DY-500 class ship:
IRK: An old Earth vessel, similar to the DY=500 class.
SPOCK: Much older. DY-100 class, to be exact. Captain, the last such vessel was built centuries ago, back in the 1990s.
So it is unlikely that more than one or two later classes of DY ships were available in the 1990s. Khan would take the most advanced ship he could get.
And:
MARLA: Captain, it's a sleeper ship.
KIRK: Suspended animation.
MARLA: I've seen old photographs of this. Necessary because of the time involved in space travel until about the year 2018. It took years just to travel from one planet to another.
So it took years to get just from one planet to another during the 1990s. Neptune orbits the Sun at a distance of 29.81 to 30.33 Astronomical Units (AU) while the former planet of Pluto orbits the Sun at a distance of 29.658 to 49.305 AU. A light year is 63,421 AU and Alpha Centauri, the nearest star, is about 4.3 light years from Earth, or about 5,531 to 9,195 times the distance to the farthest planets in our solar system. Thus it should have taken thousands of years to reach even the nearest stars with the ships available by 2018, and so no colonization of other stars should have been possible in the 1990s.
Of course, I did once have a theory that in Star Trek Earth discovered methods of faster than light (FTL) travel twice. The first time a secret group secretly built starships and left Earth to explore and to settle a colony in another star system from which they continued to explore the stars, leaving no record of this on Earth. Tarbolde who wrote Nightingale Woman on the Canopius Planet in 1996 was probably one of them. The Valiant was one of their ships.
Meanwhile on Earth the Eugenics Wars happened and interplanetary travel took years, and Khan left Earth in suspended animation hoping to reach another star.
In 2018 Earth based space travel got much faster, so Earth developed FTL star travel for the second time in 2018 or later, and began to explore the stars, and eventually the explorers from Earth and the explorers from the Earth colony met and united sometime before Kirk's era. If one group had "broken the time barrier" and the other hadn't, the reunion might have happened between the departure of the Columbia and "The Cage".
When I believed that all dates in Star Trek were given as Anno Domini dates, I calculated that the Valiant should have been voyaging sometime between AD 1896 and AD 1996, so I came with with the theory that Earth discovered FTL interstellar travel twice, and the first time it was kept a secret from the rest of Earth.
But now I believe that Earth dates in Star Trek are given in several different dating systems, so that the year 2100 in one story is not necessarily after the year 2000 in another story. Thus it is not no necessary to assume that Earth developed FTL star travel twice, though some Star Trek chronologists might find it useful.