When you get to Rapture, Elizabeth explains it by saying it’s another possible universe. Okay, I thought, we’re simply playing in a different game universe accessed via lighthouse, and didn’t really think about it much past that.
What I failed to realize is what she really meant. That Rapture, and really all the events of the original BioShock are direct, alternate parallels of everything that happens in BioShock Infinite, right down to the characters themselves.
The proof that can’t be overlooked? In the original BioShock, it’s made expressly clear that only Andrew Ryan himself can operate the Bathyspheres in the city once they’re on lockdown. Part of the twist of that game as that you can also operate them, and you eventually discover than you, as Jack, are Andrew Ryan’s illegitimate son (or probable clone) which allows you to use them yourself.
In Infinite, you’re operating them once again.
The implication here is that DeWitt/Comstock is Jack/Andrew Ryan .