Has anyone heard why the third movie - Harry Potter And The Prisoner Of Azkaban- isn’t going to come out until late 2004?

I thought it was a little strange when I saw a November 2004 date for it here.

But I checked imdb and they give the same date: here.

The only article I could find says that it starts shooting in January, but doesn’t say why the anticipate the movie will take nearly two years to complete . I thought, when the first movie was about to be released last year, that I heard that they were planning to release one movie a year, like the LOTR trilogy intends to.