I dont know either but I can tell you it doesn't mean zone office show car. That code does mean something like that but not on a Regal. I have ran across quite a few stray codes that aren't in the books. They seem to be on a lot of Canadian spec cars but I have found them on US spec cars too. Another really common one I see a lot is the code Z09. I'm guessing its a code for a certain option content or combination of codes. It would be nice if you had the build sheet for your car as that might help explain it. I was parting out a 84 hot air Riviera a while back and I found one of the build sheets for it. What was strange is that the car was delivered to Buick Motor Division in Flint MI. Normally you would see a dealers name in that spot. No weird code like ZR6 on the label anyway. It was an early production car so maybe some one with some pull in the big office ordered it. Have any idea who the original selling dealer was?