As I mentioned in the Trivia section, author Kyle Higgins specified that, of the Batman Beyond comic book series, Hush Beyond is the only one in continuity with the mainstream DC Universe. The other series, while also including the events of Hush Beyond, form a separate timeline. So, essentially, Hush Beyond is a separate universe, serving as a possible future for New Earth, while Earth-12 is a separate continuity, blending elements of New Earth and the DCAU. Even the DC Wiki treats them as separate worlds, so in my opinion the pages shouldn't be merged.
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