I would just like to add to this, that for the duration that SG-1 and Atlantis were running simultaneously, the new episodes themselves ran in parallel. SG-1 season 8 and Atlantis season 1 each released new episodes on the same night (two part season openers not withstanding), back-to-back. And while rare, they will later on make direct references to things happening episode-by-episode in the other.
I would just like to add to this, that for the duration that SG-1 and Atlantis were running simultaneously, the new episodes themselves ran in parallel. SG-1 season 8 and Atlantis season 1 each released new episodes on the same night (two part season openers not withstanding), back-to-back. And while rare, they will later on make direct references to things happening episode-by-episode in the other.