I don’t think of Plan-Do-Check as a lifecycle – it abstracts over levels of design abstraction, which are usually explicit in a lifecycle model. But OK, I agree with your point – in the original V model, there’s no explicit “Check Your Plan” activity, and if it’s implicit, it’s probably implicit within the “Plan” activity.
Still, I think if you admit the Fractal extensions to the V model, you are then free to think of a “Check Your Plan” activity as being either in the “Plan” activity (X)OR the “Check” activity. I think the better choice is to regard the original V model “Plan” activities as really being little micro-V Plan/Do/Check(-Your-Plan) iterations with null “Do” steps.
At this point I feel like I’m arguing about how many angels could fit on the head of a pin. Maybe that’s a sign that I’m pushing this point of view a little too far!