Extra Quests After SoA Missions

I would like to upgrade my SoA ring to the +1 version. I read that part of the pre-requisites require having done (practically) every single coalition assignment. Since the various frontier stations have already been established, this means that certain assignments are essentially locked out to anyone who only recently obtained the SoA expansion. Base provision assignments (Courier's Coalition) are no longer available (and will only become available if we should lose the various Frontier Stations -- highly unlikely).

So does this mean those who came late won't have access to the +1 rings (and Ygnas cipher)?

Those don't count towards the total.

Glad to hear that!