Not as explicitely, for ship missions, and (if my failing memory still works here) maybe also before the Panther Clipper update - but I alweays thought the number shown on the mission board would relate to the available missions on the sub-board. Always had the feeling I was short-changed here, but these days had a couple of occasions with 5 missions shown on the main mission board screen, but only three available inside the sub-board. Or six missions shown, but only three in the sub-board and all of them blocked for missing rep.