This all comes from the way that morph slaving was implemented, e.g.:-

                     valueOpDeltaAdd
                                Figure 1
                                BODY:2
                                SuperHero
                        deltaAddDelta 1.000000

Everywhere else that a part of one model points to a part of the same or another model (ordinary parenting, IK-parenting), it does not state the name of the model pointed to but indicates which model by the colon-and-suffix number on the part name. It is a pity this was not done here also. But that is "water under the bridge" and we are stuck with the method that we have, for now.