Why does the movie feel the need to make Anne the older sister?

Rating: 7/10 (18 July 2008)

Pretty decent movie, but there is one thing I just don't understand. Historians seem to be pretty much in agreement at this point that Mary was the older sister of Anne, not the other way around. Despite that fact, this movie goes out of its way (way out of its way) to set forth repeatedly that Mary is the younger sister. Twice Anne calls her "my younger sister" and once the King says something about what it is like to be in the shadow of her older sister. The thing that is bizarre about this is that it adds absolutely nothing whatsoever to the movie--it's not important to the plot and is essentially unrelated to the story. So, the movie goes out of its way to establish something that isn't true, and even if there is legitimate dispute on the issue, why not just steer clear of the topic altogether? There was no point to or reason for the movie going down that path at all, so why do so?