Just to put closure on this, here's the notification sent to dealers. Literal interpretation, starting with VIN N678254 all cars had them.
The labels were supposed to self-adhere but quickly fell off. Chevy added the Mylar overlay, solving the problem.
There is no way to pinpoint exactly when the labels entered production. Cars were not built in VIN order; 08E spans Aug 26-Sep 3. Some or all cars built during that span had one.