By adding the process of grieving the decision of the PCRC—which isn't a decision, but a recommendation; it's the outcome of the PCRC's investigation—it adds a grievance recourse before the final decision has been made. The final decision rests with the deputy head.
It makes much more sense that a grievance follows the decision about what the deputy head does with the recommendation of the commission. There could very well be circumstances whereby the commission makes a recommendation that the deputy head doesn't act on, so there would be no reason to grieve a recommendation that has not been acted on by the deputy head.