LOPA,
They do change, as i am aware, no first officer is moving from the 767 to the 787, all the FO's to the 787 will come from the 737, looking at 6 of the 78's arriving this year and a fleet requirement of 8 FO's per aircraft, you are already looking at 48 people moving from the narrow body to the wide body, they have to be replaced, don't they? Then there are the senior Embraer FO's who are moving straight to the 777, and there's two more 77W arriving this year, the numbers you are talking about are not taking all this movements into consideration.
Someones got to keep the E jet and the 737 fleet flying. Mark you, despite the moving of the 73 classics to Jambo jet, the union has insisted their crewing has to be with KQ pilots.