the fuck you mean by "outdated artstyle"? how the fuck does an artstyle gets outdated?
As Runey has continued working on the game, gaining a better understanding of scene composition or through a higher efficiency with the tools being used, he's able to produce scenes of greater quality. When he goes back and re-animates or brushes back over a scene, they don't take as much time as it would for a new scene; as he already has the layout, plot, and angles already setup. He just goes through and reworks them to bring them closer to the quality presented in the rest of the work. I believe this to be a good thing, as not only does it round out the experience for us the players, but it also allows the game to come closer to Runey's final vision of the game.
TL;DR - Reworking a scene takes a fraction of the time of a new scene, and reworking brings the quality of old scenes to match the new and ultimately rounding out player experience.