It's a fixed, NOT-alterable timeline...
That's the biggest twist of the movie. The final surprise.
The Temporal Agency is a "trick". The Agents believe to be changing the past (in order to improve history) but in truth they don't know they are just fulfilling their predestined roles in the past events.
It's a fixed timeline, like 12 MONKEYS (the movie) or TERMINATOR 1. A casual loop.
There was never an "original timeline". The paradoxes always happened the way they happen in the movie.
The NEWSPAPERS CLIPPINGS coming from "different iterations of the future" were FAKE. Maybe the Temporal Agency did that. Maybe the crazy and old Ethan Hawke did that. Or maybe they were an "ARTIFACT" which never had an origin, because Young Ethan Hawke took them from old Ethan Hawke and so on and on and on and on.