Pole shift,
Many of the Fo's are proven, experienced aviators with 5000-10000 hours and several thousand hours PIC/Airline command to boot. They just lacked the right typerating or else they would be sat direct in the left seat with that experience.
So tell me again why a DEC that joins at a later stage should jump the que?
And ofcourse a DEC will not move backwards
. He keeps his number like everyone else...