Subtext of a throw-away line.
In the 'Star Trek: the High Frontier' campaign's one Mirror Universe episode, called 'Pressed Against the Glass', the mirror counterpart of the PC CO in the game, Captain Ariel Ibanez (although, actually, he was 'Admiral' Ibanez in the mirror universe), made the throw-away comment that, for me, defines where Enterprise is in my game. In a personal log that opened one of the Acts of the episode, he said, as an aside comment, that 'Archer was right. We should have learned, like he did, from his mistakes, and shut our doors when we had the chance.'
In short, my campaign's contention is that Archer's timeline is our Mirror Universe. :)
I have since gone on record, yes, as telling that to my players, and making it official. The more I thought about it, the more it grew on me.
CmdrBJ