New Earth was a unique universe, as it was an amalgamation of Earth-One, Earth-Two, Earth-Four, Earth-S and Earth-X as a result of the multiverse partially collapsing during the Crisis, thereby creating a new reality.
The new history of the New Earth Universe was primarily the history of Earth-One, with additional aspects of Earth-Two, Earth-Four, Earth-S, and Earth-X folded in. As a result, although it superficially resembled the Pre-Crisis Earth-One, it was, in fact, a new version of Earth.
This was apparently not the case however, as other alternate universes were discovered to still exist, and even the ones that didn't, could be accessed through hypertime, because every timeline that ever existed was available to a person who used that method of time travel. This includes any timeline that existed prior to the Crisis.
- This new realty, was the mainstream reality of the DC Multiverse between 1986 and 2011, starting at the end of the Crisis on Infinite Earths and ending with Flashpoint.