Even if an officer sees the expired tag as PC to pull you over, a check with the dispatcher will show your registration to be current in the online system. Knowing that they are behind in mailing, the officer should check before making the decision to pull you over.
Maybe. If he bothers to check.
In WA State tab enforcement has been deemphasized by the WSP to the point where expired tabs are being ignored unless they really need a reason to stop (i.e. suspected criminal activity). I haven’t bothered to re-tab one of my infrequently-driven vehicles.