indeed. If you argue Omid and Christa are unknown then so is Clementine... because we don't know what happened to her after the scene in the fields.. so that turns everyone into either unknown or dead. I think you have to account for ALL the characters in the game in order to make a chance of survival.
And that would be around 1/3 characters you meet will survive long enough to finish the season. Anything else is no more than unproved guessing.