C.E. Evans wrote:
The 70-year thing isn't meant to be an exact figure, but a very rough estimate or a ball park figurew, IMO. A ship at Warp 9 or so might average about 1000 light-years per year, taking into account periodic stops whenever necessary.
Personally, I think Janeway was being optimistic. I think most ships can only sustain Warp 9 and beyond speeds for a relatively short period of time but will spend most of a voyage around Warp 6 to prevent engine burnout and to conserve fuel.
Considering Seven, made a song and dance about using Borg cartography to cut 3 years off the journey, I think it's a reliably accurate number, and as the years went on, they did reduce the number of years they expected to be in transit in relation against all their short cuts.