The developing times for rating at 400 were made with certain assumptions, we may not know what those assumptions are. However, both Tri-X and modern photographic paper have enough latitude that it's quite ok to shoot at 200 and develop at 400. You may get a little more shadow detail and a little more exposure in your highlights, but nothing that Tri-X cannot cope with.

I personally shoot at 400 and overdevelop a little bit, using the times for 800 or 640.