Ken
If the issue of a LSGC is not backdated due to cost then one can only look at the precedent of the award of the Arctic Medal and GSM for the Canal Zone together with the Bomber Command bar (a travesty). They were campaigned for over 70 years and in conclusion awarded to all ranks.
The surviving members of the Officer Corps, past and present with 15 years service would probably not require an extra "print run" of LSGCs which exceeds the 10 thousand odd Afghan medals awarded. Maybe TTN has a view.