I don’t read a lot of science fiction, but from what I’ve seen, most stories that involve time travel incidentally treat it one of two ways - either you can change the past or you can’t. In, say, Star Trek and Back to the Future, you can change the past, which leads to certain causality violations, but that’s okay, as long as you’re not in a causality-conserving universe. The only good example I can think of off the top of my head in which you can’t change the past is Hitchhiker’s Guide to the Galaxy.
So what does it mean to be able to change the past? It means that any shows that aired before you went back in time show one world, and any shows that air after show the changed world. As long as you adhere to this, you’ve got consistency, and therefore, continuity.
Now, I haven’t seen this episode, but even if the Borg make themselves fully known to humans and everything you fear comes true, it’s okay, because in Star Trek, you can change the past. “Q Who?” aired before First Contact, so it shows the old, unchanged past. Only if you can find a show that aired after First Contact (i.e. the last two seasons of DS9 or the last four seasons of Voyager) that says that the Borg were not known in the 22nd century will there be a continuity violation.
Still don’t understand what I mean? Still don’t believe that you can change the past in Star Trek? Consider the following four examples: “Yesterday’s Enterprise”, “Past Tense”, “Trials and Tribble-ations”, and Star Trek: First Contact. (In First Contact I’m talking about the part near the beginning of the film before they go back in time, when they see the changed Earth.) There are probably some more good examples in Voyager, but I didn’t see the whole thing.
The easiest example to understand is probably “Trials and Tribble-ations”. “The Trouble with Tribbles” did not show DS9 crew on K-7; “Trials and Tribble-ations” did. If you don’t buy that showing two different versions of the same place in spacetime is legitimate, how do you explain that little lapse in continuity?
