I recently had a conversation with TimeShade about my thoughts on how we should label all the Earths that were birthed after the events of Crisis on Infinite Earths crossover. I noticed pages like the New Earth-2, Stargirl's universe is named Earth-2 (New multiverse) however in light of new reasons, I strongly believe it should be named Earth-2 (Post-Crisis), same going for every other New Earth and here is why I make this argument:
1. In the episode Marathon of The Flash, that takes place after the Crisis crossover, "Earth-Prime is literally referred to by name as a "Post-Crisis World" by Killer Frost.
So, this is an official term used in-universe by a character to describe a newly created Earth rather than "(new multiverse)" that sounds more of a conjectural title in comparison to Post-Crisis.
2. TimeShade seems to agree because of this reasoning alone and I was reminded of a particular argument that said naming the new Earth pages "Post Crisis" would be "inaccurate" seeing as the Crisis was still happening after the New Multiverse was created, I thought this was a good point but then I realized, whose to say that wasn't a different Crisis? Think about it, the Crisis that we saw before the Rebirth was Crisis on INFINITE Earths, the Earths were being destroyed. Anti-Monitor's attempt at revenge on Earth-Prime in Part 5 could simply be considered a Crisis on Earth-Prime as it takes place in the new multiverse on that Earth. Similar how the events of Crisis on Earth-X took place Pre-Crisis but the events were changed to Time Traveling Nazi Invasion Post-Crisis
Killer Frost's line alone shows the writers think of the New multiverse as a Post-Crisis multiverse. Also it just sounds more official don't ya think? The DC Database wiki uses this term as well