Window sticker will tell you what it's built with from Chevy (factory). It won't tell you anything that the dealer installed (or anyone else)post delivery to the dealer. I have the same issue as I have a bunch of dealer installed items that are Chevy. Rims, Glow Tie, black out pieces and such and some not like LED lights.

 

The original window sticker lists all factory-installed options and packages, so you can compare it to what’s on the car now. If something isn’t on the sticker, it was likely added later. A detailed vehiclehistory service can usually provide that sticker, which makes it much easier to verify originality.