There is no date as of yet. There will not be a correct release date untill Square Enix says so. Gamestores are always wrong. Never trust them. They tell you a certain date, because they just want your money, and want you to pre-order the game. They could care less when the game really comes out. I know of at least six different dates so far:
June 7, 2005
September 14, 2005
September 15, 2005 (yeah, heard both dates)
December 1, 2005
December 30, 2005
January 1, 2006
Also, you can't really say that the game will come out after Final Fantasy XII. Nomura stated that before the game was delayed so much. There is a chance that Kingdom Hearts II might come out before Final Fantasy XII. We just to have patience and wait. It is better that they take a long time, and we get a good game. Where as if they rush, we might get a crappy game.