Z51 Vents
Only the Z51 contains the ducts that route the air to the differential cooler (passenger side). The passenger side vent on the base, while still there, are non-functional. The driver side vent is functional on models with automatics. The lower bumper vents and front gill vents are functional and provide brake cooling on all models.
After watching production in person, I'd suppose it's possible for one to unblock and put a differential duct on a base model. Could be an aftermarket kit available one day to do just that.