I'm not sure if this really holds up, but I thought Sarah Connor Chronicles was the same kind of time travel thing as STXI. Terminators from post-T3 (or T4?) travel back to sometime after T2 and make changes sending history down an alternate path. Just like Nero and Spock went back to Jim Kirk's birth and started meddling.
Indeed. "Continuity" in the Terminator
series is kinda slippery by design, since the whole series is about the future trying to change the past in order to change the future . . .