I'm not a Buick RPO expert but I thought I read in (my now destroyed thanks to my dog) Kirban's Guide to 1986-1987 Turbo Regals the chrome mirrors weren't optional on a WO2 car. I'd like to see the RPO decal inside the trunk. The whole idea of a WO2 car was to rid itself of the chrome accessories.
I'm in no way saying strange things can't happen with these cars. My first GN (to which I was the 2nd owner at 16,000 miles) had a "BUICK REGAL" plate above the dash. I had the car for 7-8 years before I realized it wasn't correct. In fact I had enthusiasts accuse me of having a GN clone.