Why didn't Atlantis block the superhive's stargate in Enemy at the Gate?
I don't remember this being addressed in the actual episode. If it was, please let me know.
It is established pretty early into SG-1 that when a new stargate arrives to a location, it becomes the dominant gate and blocks any other gates that may already be there.
For example, Earth used to have the Antarctica gate. Then Ra brought the Giza gate, which became dominant and prevented the Antarctica gate from being used under normal circumstances. Then Apophis brought a third gate on his ship, which superseded the Giza gate and prevented that one from being used.
So, we get to the Atlantis finale. The superhive arrives to Earth with its own stargate, which prevents the gate at SGC from being usable. Any attempt to dial SGC connects to the hive instead. Later on, Atlantis arrives to the battle, and Sheppard's team uses the gate on the superhive to escape.
But, according to the above rule, when Atlantis arrived, its gate should have become dominant, and prevented the one in the hive from being used. So how come the team used it to escape?