Now I'm not going to post the plotline on here, because it's already available on Gateworld, Wikia: Stargate, and IMDB.

But I do just wanna go over one thing and post a question, because there was a big potential continuity error which is really bothering me, and I wanna make sure I didn't just miss something.

SG-1 + Jack O'Neill (yay O'Neill!) were at a Tok'ra extraction ritual, to pull the symbiote out of what they thought was the last Ba'al (although they were mistaken).

So as his failsafe plan, the real Ba'al goes back in time via the Stargate to 1939, aboard the USS Achilles. His goal? Destroy the Stargate so that no one can use it. He fails, but he does manage to sink it so that the USAF doesn't obtain it and get the SGC up and running. This begins a series of events in an alternate timeline. At this point,

Original Carter - Alive. Went back through the Stargate and ended up in the sunken Achilles on alternate Earth.

Alternate Carter - Astronaut. Dead in a space shuttle crash landing.

Original Jackson - Alive. Went back through the Stargate and ended up in the sunken Achilles on alternate Earth. Lost his leg to frostbite.

Alternate Jackson - Alive. Discredited author and archaeologist living on the fringes of society in Egypt.

Original Mitchell - Alive. Went back through the Stargate and ended up in the sunken Achilles on alternate Earth.

Alternate Mitchell - Non-existant. Ba'al killed Mitchell's grandfather aboard the Achilles, causing a grandfather paradox in which Mitchell does not exist.

Original O'Neill - Dead. Killed by a clone Ba'al at the extraction ceremony when he attempted to escape extraction.

Alternate O'Neill - Alive. USAF officer who does not believe the story that original SG-1 is trying to tell him about the original timeline and their origins.

Original Vala - Vanished. Disappeared from the extraction ceremony when the timeline was altered.

Alternate Vala - Alive. Host to Qetesh, Ba'al's queen and murderer.

Original Teal'c - Vanished. Disappeared from the extraction ceremony when the timeline was altered.

Alternate Teal'c - Alive. First prime to Ba'al.

So my question is this: Carter, Jackson, Mitchell, and O'Neill all continued to exist (or in alternate Mitchell's case, didn't) in their own ways in each of the timelines at this point. But why didn't Vala and Teal'c? Logically speaking, if there is an original and an alternate of each, then the originals should have stayed existent and not vanished (along with the Tok'ra who disappeared, and their buildings), while the alternates filled their roles as they should have. Except for Mitchell (as a result of his grandfather paradox), each one of them should've, at least briefly, existed twice simultaneously.

So why was the story written this way? It's a huge plot hole, and it's been bothering me, cause it's not the kind of detail usually left open by the team behind Stargate. So was there something I missed that explained this? Or was it simply dramatic license for good storytelling? I'm hoping it's not the latter, because I would be severely disappointed in a usually consistantly explained story. 

There's only one other detail of this magnitude I've ever seen them ignore for storytelling purposes. The first is the fact that much of the universe speaks English even though they should speak some derivative of Latin or Egyptians (since it all originally came from the Ancients and Goa'uld). And that one they even attempted to explain well enough for me to put it out of my mind.

So why this one?