Re: Is everything before the destruction of the kelvin exactly the sam
What you've just said is exactly what I covered under the theory that the '09 timeline "branched" instead of always existing in parallel to the Prime timeline and being identical up to the point of Nero's incursion.
There could be an infinitude of timelines that are all essentially identical to both the Prime timeline and the '09 timeline of course.
Data's head wouldn't "vanish" from the cave; it would never have been there to begin with. And AFAIK we can't know whether in the '09 timeline we saw it ever was there because we have no clear evidence of temporal divergence that could be traced to those events.
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