They are looking at the wrong diagram. Tell the parts counter to pull up the diagram that shows the front fender liners. You can clearly see the outer valance with two screws. My dealer tried to tell me the same thing. BTW, the part number is for both valances and 4 screws. It's a kit.
Don't let them push it back on you and don't pay for them yourself. They should have been installed on the car and someone along the way messed up. The dealer should be held accountable.