John's timeline changed when he entered into the flux, this time-frame paradox, would never be the same as the one he knew before you leaped.
Thus it altered this reality, to someone else's;vice-versa... Which is why he got stuck here in the first place.
When john was in tampa, at mac dill airforce base in the early 2020's, he didn't realize that the 177th division would ultimately falter and the time leap would be halted another 60 years, switching the quantum leap int a freeze-point matrix.
Thus when he was born, another would be born 4 year before him in the same city, also baring the same qualities.
If i'm correct, the john titor you know, wouldn't be john titor at all, it would be a completely different person.