The Serpent's Lair (3) - S2-E1
Question: OK, so we're all familiar with the whole 'gate priority system, which was ignored by the producers so they could give Earth a second Stargate for some epic foreshadowing of the episodes Nemesis and Redemption Pt. 2. So here goes. Why, when you take that gate priority into consideration, was the SGC able to gate to the Alpha site to start evacuating the "best and brightest" when the 'gate Apophis brought to Earth, presumably to block any outgoing wormholes, had a DHD hooked up? I get that it was necessary to give Daniel and the scum-sucking, overdressed, boom-box-voice, snake-in-the-head, seventh-on our-increasingly-long-list-of-dead-bad-guys (as of Threshold) a way off the Ha'tak before it exploded, but its functionality should have said "NO!" to the SGC's attempts to gate out.
Answer: The gate with priority is the one that will be activated when gating TO Earth. You can still gate out with any available stargate. The plan to prevent escape involves Apophis dialing from his Ha'tak so that a second wormhole can't be opened from SGC.