In the movie it is stated that V’Ger, Vyager 6, fell into a black hole ending up at the AI/Thinking Machine planet.
Which is my point - assuming Voyager 6 was traveling at the same rate as Voyager 1/2, there would need to be a black hole within five light-days of earth...unless of course the black hole was used to somehow send the upgraded voyager back in time to 2271.