New Earth is the post Infinite Crisis Universe. Zero Hour wasn't a destruction, really. Or was it? Who knows? Who remembers?

Zero Hour was - like Flashpoint, a rewriting of the timeline - not a multiversal upheaval like CoIE or Ifinite Crisis.

Events that revised the DC Multiverse:

Crisis on Infinite Earths, Zero Hour, Infinite Crisis, Flashpoint, and probably Convergence.

But the thing to be aware of is that "New Earth" was not destroyed at any point between CoiE and Flashpoint. At least... I think that's true.

I think New Earth was diverged, according to how the "rule" of time travel works in comic books.

We have to wait and see what Convergence is all about and how it will come to term with the DC Universe's status quo of Post-Flashpoint and its timeline inconsistency (namely Batman's history and Green Lantern arcs).

Question: Even in a comic book, when the known past is altered, whether by time travel or by a temporal event, isn't it still technically a new universe in the aspect that it no longer resembles the previous one?

Answer: No. It may be considered as such, but, if there is no clarification that might indicate that the events are not part of the current timeline, then it is the same universe and it might just be "editorial mistakes", known also as inconsistencies. Assuming stuff, would only end up confusing people, IRL too.

That's kind of how it worked in the Marvel Universe, isn't it? For example, when Count Nefaria turned up alive after being considered dead for so long, it turned out there were just mitigating circumstances behind the scenes we were not aware of.

So, is this more accurate?

Pre-Crisis Universe
Post-Crisis Universe/Post Zero Hour Universe
Post Infinite Crisis Universe/New Earth
Prime Earth