Other mistake: At the very beginning when the scientists have uncovered a new chevron, it's the "Earth" chevron; a triangle with a circle on top, which indicates the planet of origin of the wormhole. However, ONLY earth should have an earth chevron - all other worlds have their own symbol.
Other mistake: In the last few minutes of this episode, Carter uses the DHD to dial home. She enters the first chevron, then the "Cannon" dies. And when she proceeds with the dialing,the first chevron is still encoded, and you can hear that she enters seven additional chevrons, which gives an equal of eight chevrons, and then engages the stargate. That would mean they are in another galaxy, referring to S02E15. In that episode they tried to dial the eight-chevron address from SGC but the computer wouldn't accept it. So, it is impossible that they would be in another galaxy.