By going back in time and altering things Nero created a divergence point in the timeline. The timeline was the Prime one until it split. It wasn't previously existing, like "In a Mirror" (which would have created a split in the Mirror Universe when Defiant arrived)
Yeah, I agree that pre-Nero arriving it was TOS.
I was just saying that the alternate universe all along angle is much more sensible than TOS Spock goes into a black and hole and is replaced by a different Spock from a different universe who arrives in a different universe that was triggered when Nero had arrived in a different universe and created a different universe when he destroyed the Kelvin.