Bulldozer has NO official release date. Nor should you expect a date from AMD given how they handled Llano (no official advance announcement of launch). They have provided a month at Computex for FX launch and that month is August.
The Sept 19 date, along with Sept 6th and Oct, are all rumors that came from either Kyle Bennett, OBR, or the FX comic/animation.
.... And then those dates got repeated and repeated and repeated to the point that everybody believes them