imho a small change such as lights, bumper style etc doesnt mean that it is a new Mk only that it is a new series of the current Mk.
Vauxhalls usually have a mid life facelift, where the bumpers, lights, wing mirrors, spoilers etc of the current model are revised to produce a fresher version of the current model but the Mk doesnt change
i.e, both are the Vectra C