It's just your statement made it seem non-branching methods of time travel have been confirmed and I think that's unclear.
In previous time travel episodes out heroes return to the same universe they left. In First Contact, the present changes due to the changes in the past. The Enterprise hadn't gone anywhere yet they saw the change on Earth. Once they went back and returned, the present was restored. They didn't return to the present where the Borg had taken over Earth. If the Borg going back in time had really created a new branch, the Enterprise would never have known it.
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