Wouldn’t Enterprise technically be an alternate reality than the normal Trek series? I mean, it’s pretty much confirmed that it takes place after the skewed events of First Contact. Either they pulled a Back to the Future and history was ‘re-written’, or the events of First Contact/Enterprise actually happened in yet another separate alt. timeline.
The first rule of ST time travel mechanics: Don’t talk about ST time travel mechanics. 😛
Seriously, though, the consequences of time travel have never been portrayed consistently across the different movies and series or even different episodes within series. Sometimes the Novikov self-consistency principle is in effect, other times it isn’t; sometimes alterations made to the timeline will re-write the original timeline, other times it’ll create a whole new timeline separate from the original; sometimes time travellers into the past will replace their past selves once they arrive, most times they won’t. The discrepancies are myriad.