I don't see the Borg Queen as a continuity error. The Borg only appeared a couple of times before First Contact so we knew very little about them to begin with. It's not on the scale of the Xindi taking a chunk out of Earth or Archer defeating the Borg 200 years before Q Who and none of this being mentioned later on.
What the Borg Queen is is an enormous plot hole. If she was around at Wolf 359 what did the Borg need Locutus for? Though even that can be easily reconciled by the 2 part episode Scorpion in which Seven Of Nine is used as a spokersperson for the Collective despite the fact we already knew about the Queen at that point. Maybe she only appears on special occasions.
What the Borg Queen is is an enormous plot hole. If she was around at Wolf 359 what did the Borg need Locutus for? Though even that can be easily reconciled by the 2 part episode Scorpion in which Seven Of Nine is used as a spokersperson for the Collective despite the fact we already knew about the Queen at that point. Maybe she only appears on special occasions.