Multiverse/parallel universe concept helps iron out the continuity problems with most time travel fiascos.
The problem with ENT Regeneration line about it make take 200 years to reach the delta quad. Is that its a detail that the writers came up with to fill an undefined area in 2003 from an episode (Q Who) which was aired in 1989. Retcon i think is to strong a word but it may apply here. It's similar to what George Lucas did with the Star Wars prequels and how the details of Anakin's training, Anakin's fall to the dark side, the clone wars, Luke and Leia's family details were retroactively explained decades later.
You can watch TNG "Q Who" and "BOBW" without ever watching ENT "Regeneration" and you would know that the reason the Borg invaded Federation space was because of their initial encounter with the ENT-D . How they damaged a cube, and miraculously (thanks to Q) escaped a pursuing cube. Jean-Luc Picard was kidnapped and made the voice of the Borg because of his status as captain of the flagship of the Federation. Information the Borg drones who absorbed the date from the ENT-D's computers and Q Who would've gathered and processed and sent throughout the collective.
As a timeline though it should work like this
Q Who : First Contact with the Borg
First Contact film: Time travel changes the past several times