Doc Scratch said that the Alpha Timeline was the timeline uniquely containing his birth and death. Since we've already seen both his birth and his death, how is, e.g., the Game Over timeline somehow not contain them? (This logic seems like it should hold for ANY doomed timeline which diverges after we see Doc Scratch's birth and death -- and thus which we know must contain them, right?)

It’s likely similar to how the trolls couldn’t talk to the kids in their doomed timelines. So that if any doomed timelines occur he is no longer able to interact with them and characters in it can not interact with him.

Once we get to the likes of GAME OVER though, retcon abilities start coming into place which ignore predetermines rules of Space and Time so shrug.png