How could the timeline shown in ENT lead into the TOS+ one, when ENT was specifically a continuation of the alternate history created in First Contact, when the Borg tried to stop Zefram Cochrane's warp flight? I've often wondered if Seven of Nine originally existed prior to the events of FC, as that movie did appear to make out that humanity became aware of the Borg much earlier, which may have been what led to the Hansens setting out to study them.
Because FC isn't an altered history. It "always" happened that way, the Next Gen crew just didn't know it. Take a look at this scene from "Relativity" ...
DUCANE: Let's see how much you've assimilated. The Dali paradox.
SEVEN: Also known as the Melting Clock Effect. It refers to a temporal fissure which slows the passage of time to a gradual halt.
DUCANE: The Pogo Paradox.
SEVEN: A causality loop in which interference to prevent an event actually triggers the same event.
DUCANE: Excellent. Can you give me an example?
SEVEN: The Borg once travelled back in time to stop Zefram Cochrane from breaking the warp barrier. They succeeded, but that in turn led the Starship Enterprise to intervene. They assisted Cochrane with the flight the Borg was trying to prevent. Causal loop complete.
DUCANE: So, in a way, the Federation owes its existence to the Borg.
SEVEN: You're welcome.
Seven learned that from the USS Relativity's computer, studying for her mission into Voyager's past. The 29th century Temporal Integrity Commission scan time as easily as the 24th Century Voyager scans space, they would know if history had been altered. Furthermore, it's the writers explicitly spelling out their intention.