So does this retcon how Khan comes to power in the 1990s and pushes the eugenics war further in the timeline? I have seen some people say this was done to keep the timeline consistent with ours.
Key events are preserved but the details may change and slip a bit. The details can include slippage in the dates.
The 90s date was implicitly overwritten by TNG’s premiere where Roddenberry himself decided to shift WW3 to the mid 21st century.
People had head canoned the link between the Eugenics wars and WW3 out of existence, while also ignoring that TOS implied Warp was discovered in the late 20th century.
Accepting that temporal incursions alter the Prime Timeline just makes sense of events like Voyager Endgame.