Once More Through Time III

I know the answer to the question: What would happen to da Vinci's timeline if he did return to it with some knowledge of relativity? See the previous post. Of course, if da Vinci had had such knowledge, then that knowledge in his head would have caused some changes to history. But we also know that he did not have such knowledge.

Let me present a speculative example:

in 1940, British Intelligence secretly sends agent x to assassinate Hitler;

x's colleagues legitimately speculate about the consequence if x succeeds;

x is never heard from again and Hitler remains alive until 1945;

in 2020, an archivist discovers for the first time documentation of x's mission;

the archivist legitimately speculates on what would have happened if x had succeeded;

however, we do know that something caused x to fail even if we still do not know what caused his failure;

we cannot now ask, "What will happen if x succeeds?";

in an immutable timeline, the above reasoning remains valid even if x was a time traveler who had departed from 2020 and arrived in 1940, then set off on his secret mission.

Da Vinci did not return to his period of his timeline with any knowledge of relativity because Taverner prevented this from happening. But the following combination of events:

da Vinci came to the Old Phoenix from a timeline in which he never had any knowledge of relativity;

da Vinci returned to his timeline with some knowledge of relativity -

- is contradictory and therefore cannot happen. And we happen to know that it was Taverner's intervention that prevented da Vinci from gaining some knowledge of relativity before returning to his timeline.