So can future indoc classes only be awarded left over vacancies from the current bid or can they go back further?

Also, can the vacancies created from the current bid then be offered to new hires or do they have to have another vacancy bid?

Example: say after all is said and done there are 10 756 FO DCA positions left vacant by people moving up or to another airframe. Can a new hire class be offered those DCA slots without another bid therefore preventing a current 757 FO at another base from moving to DCA?