This deserves a lot more looking into. Possibly a post in c/DaystromInstitute at some point, but, like Holmes, I cry out for more data before wanting to form a workable hypothesis. As a side note, I’m already gathering data for working out Una’s chronology. It’s filling out nicely.
We don’t disagree in broad terms. I just recoil from the easy (and potentially dismissive) answer if I don’t think it’s actually necessary for the most part, so I’ll stick to not futzing around with established dates until something really tells me otherwise. As someone who’s been playing around and figuring out Trek chronologies since the early 90s, this is where I’m most comfortable being.
A general observation: I think that this episode is consistent with the way time travel is seen to work in the Trek universe - that the timeline is overwritten rather than branched. The Kelvin Timeline remains the one sole example of a branched timeline that was created as the result of a temporal incursion. In all other cases, the timeline becomes (in my favorite comparison) like a palimpsest.