The DS9 revisits to the Mirror Universe (Mirror Universes?) seem to happen differently, then, because heroes whose Mirror counterparts are dead and buried (blown up, vaporized, hacked to pieces, whatever) can use the transporter trick to enter the Mirror realm; also, heroes can meet their Mirror counterparts...
We could argue all sorts of things, such as Mirror Kirk having his transporters rigged so that they refresh his clothing on every trip (and/or strip any female companions of excess clothing material). Ultimately, though, "Mirror, Mirror" is pretty much a standalone story that doesn't dovetail well into the DS9 follow-ons.
Timo Saloniemi
