I would assume that the whole reason why the VOY producers gave the ship's class as "Intrepid" was precisely because of that scene in TNG. And I'm not sure why there's an assumption that the prototype for the Intrepid class would be in drydock under construction. We don't know how old the Intrepid class is; we only know when the U.S.S. Voyager was commissioned. For all we know, the Intrepid could have been built during TNG's 3rd season.