Later in the interview, Knoll admitted to taking some creative license in this latest version of Darth Vader, saying:
“I figure he’s got more than one version of those outfits. The reason the armor looks a little grungier and dented up in A New Hope is you’re not going to wear your nice armor into battle. You’re gonna wear your beater armor into battle. Then, if you’re going to go talk to the Emperor or something, you put on the nice shiny one, show some respect.”
Darth Vader’s entire presence in Rogue One was always meant to be a direct contrast to the Imperial’s logical thinking given they have no real understanding of the Force (yet). In that regard, Vader’s evolution via his “uniform” presents an opportunity for filmmakers and fans to have yet another tidbit that makes Rogue One a unique piece of the Star Wars puzzle.
By changing small things to major, recurring characters, Rogue One has the chance to exist within and outside of the existing mythology. With the film projected for upwards of a $300 million dollar opening weekend, surely there will be plenty of fans discussing Vader’s wardrobe change and what new meaning it could present for the original trilogy.