When we first released the Prospect Guide, the book came out at the end of January, or early February, closer to Spring Training. We had the later release date originally in order to get the most moves into the book as possible. We switched from that method after the first two years, pushing up the release date of the book to early December. This was in order to get the book out in time for PirateFest one year, and for Christmas sales every other year.
The problem with this is that we missed a lot of good info with the book, and left it open to the possibility that it could be somewhat out-dated by the time Spring Training came around.