My gut tells me that, in the Trek multiverse, there is a difference between timelines (emanating from a specific universe based upon actions within that universe that effect causality) and universes (a near-infinite collection of universes all breaking off from the Big Bang). Different universes have different quantum signatures (although, not necessarily), but timelines emanating from the same universe (Yesterday's Enterprise, Time Squared, possibly the Kelvinverse) do not.
The mirror universe and the Parallels parallels were not shown to be caused by an external factor, unlike almost every other alternate timeline/reality/universe in Trek. They might be identical to the main Trek universe up until a certain point (The Borg take over Earth, the Roman Empire never falls, Worf gets a different cake), but this point was not affected by temporal indiscretions. Just by the quantum signature of the universe making quantum changes along the way.
Now the Kelvinverse has all the people who argue that it is not a rewriting of history (like Yesterday's Enterprise, Time Squared, Children of Time, much of the Temporal Cold War, etc.), but the creation of an alternate universe. It might be meaningless, since we suppose that an identical Prime universe continues to exist. It's possible that the red matter made it into a new universe (whatever), and explains why Spock and Nero never faded or flickered away. In that case, they might have different signatures.
I don't pretend to know the science behind any of it, and I'm probably forgetting some important detail in Trek's contradictory history of time travel. In another universe, I probably voted the correct way.
The mirror universe and the Parallels parallels were not shown to be caused by an external factor, unlike almost every other alternate timeline/reality/universe in Trek. They might be identical to the main Trek universe up until a certain point (The Borg take over Earth, the Roman Empire never falls, Worf gets a different cake), but this point was not affected by temporal indiscretions. Just by the quantum signature of the universe making quantum changes along the way.
Now the Kelvinverse has all the people who argue that it is not a rewriting of history (like Yesterday's Enterprise, Time Squared, Children of Time, much of the Temporal Cold War, etc.), but the creation of an alternate universe. It might be meaningless, since we suppose that an identical Prime universe continues to exist. It's possible that the red matter made it into a new universe (whatever), and explains why Spock and Nero never faded or flickered away. In that case, they might have different signatures.
I don't pretend to know the science behind any of it, and I'm probably forgetting some important detail in Trek's contradictory history of time travel. In another universe, I probably voted the correct way.