Darth Vader's costume has never been quite a set thing. While to most it looks the same, in all three of the original trilogy movies the suit had slight variations. Rogue One: A Star Wars Story is no different.
Speaking to CB, VFX supervisor John Knoll talked about bringing the villain back, and how he changed tiny details. He said:
If you look in New Hope, especially like that white corridor scene at the beginning you can see all these smudges and all these fingerprints on there because it was cast from a clay sculpt. Then by the time we got to Empire Strikes Back they made a new one that was like really polished and smooth and shiny and perfect. The chest plate is different in every film. We matched more the, what the chest plate looked like in Episode IV, but a little bit more of the high polish that's in Episode V.
Making any changes to the character could have been controversial, but this seems like very fine brush strokes. I can't wait to see Vadar back on screen.