I understand that the number that have completed the command development course to actually getting through to a command course is more like 85%.
Jet2 have ALWAYS tried to place people where they want to be, if you get an upgrade and have to move away, well that's where there is availability for you, I can only assume that a new recruit would be given a place based on where they have been told prior to an FO being offered their upgrade. Just the way the cookie crumbles.