So... am I the only one that thinks Cochrane's flight was a temporal paradox in the regular universe, and not in the mirror universe, and right there we have some differences?
Interesting, why do you say that? I find your views intriguing and I would like to subscribe to your newsletter.
Well, here's my thinking:
In "our" Trekverse, Cochrane's warp flight was said to be a part of a "pogo paradox" where an effort to prevent a past event actually causes said event. (VGR's "Relativity.") Whether you want to believe it is or not is irrelevant; Seven said it on screen. We might choose to interpret that her view of the events were Borgfacts-based; OTOH, Lt. Ducane of the
Relativity didn't correct her either. Now, there are varied ways to interpret this. Cochrane might have been able to actually accomplish the flight and make First Contact on his own; then again, he might not. Either way, the way "our" universe records it happening and the way it "actually" happened are different.
There's no 24th century
Enterprise to travel back in time in the mirror universe. DS9's mirror eps pretty clearly establishes no Starfleet and no
Enterprise. (And no Lieutenant Yar, and no vaccine!

) Presumably, the
Enterprise-
D never existed either, and was never fled into the path of that cube by Q in 2365.
Cochrane's warp flight still happened in the mirror universe, under visually similar circumstances, although apparently without a Borg attack or the presence of the
Enterprise-E since in the mirror universe there was no
Enterprise-E. Yet, he still did it and presumably "their" history recorded the actual specifics the same was as "ours" did, sans Riker and LaForge. And then, of course, Cochrane and company raided the Vulcan ship.
Presumably, there was no Borg debris in the mirror universe from the Queen's sphere to be discovered to attempt to contact their past Delta Quadrant counterparts. So in the MU, "Regeneration" never happened and the mirror Borg may have never been interested in travelling to the Alpha Quadrant in the first place.
So in summary:
- In both universes, Zefram Cochrane launches his Phoenix test ship from Bozeman, Montana in April 2063.
- Both histories record Cochrane making the warp flight the same way and attracting the attention of the Vulcans
- In "our" history Cochrane had help.
- In "their" history Cochrane did not have help.
I guess the big question is: could "our" Cochrane have launched his ship without Borg interference and the
Enterprise's help? If so, there are no differences. If not, there are already fundamental differences in the two universes.