I'm pretty sure the FC divergence point idea is from Shatner/Reeves-Stevenseseseseses Spectre
or Dark Victory
. A coin toss by Cochrane as to whether to te the Vulcans about the Borg or not.
As for "In a Mirror, Darkly" - remember that nasty regimes throughout history have rewritten literature to suit their causes. The same could easily be true of the evil Empire. Thus, the Phlox/T'Pol chitchat may not be indicitive of an earlier divergence point.