Didn't Liz drown you at the end? You're supposed to be a baby at that time, no?
Booker/Comstock was a soldier in the US army during the 1890 Wounded Knee massacre. He was invited to be baptised in the aftermath. One Booker ran from the baptism, had Anna, and become an alcoholic gambler. The other Booker accepted the baptism, because a pious zealot known as Comstock, and founded Columbia.
On another note, we've always considered Comstock's "prophecies" as simply shit he saw through the Luteces twins device. Was this explicitly explained via voxaphones? I was under the impression that the Luteces' space/time tear device did not come into being until Columbia was already founded and Comstock was considered a prophet, and was then used by Comstock for greater insight into the world as well as nab Anna.
I say this because it would explain Comstock's original visions. At the end of the game when Elizabeth confronts Booker (twice, I believe) with the post-massacre baptism, would this not cause a minor convergence of memories? Yes, it's in the "past", but Booker had been taken there symbolically
and had seen all the "prophecies" in their real form. He'd been to Columbia. He'd seen New York on fire. And he knew Elizabeth. Being in the same place/time/universe as original Booker, symbolically as Booker, would bestow confusing memories interpreted as "prophecies" on baptised Booker, granting him "visions" of a city in the sky.
It's circular.