Even my SS on that vin website shows mine to be a Z28. Shoot...my insurance thinks my car is a Z28.
There's two solid ways to tell.
1. Call SLP in Toms River, NJ and run the vin by them over the phone. They will be able to tell you (like they did for me) whether or not it's a true SS and it's build number.
2. Call a GM dealers service shop and speak to a one of the service techs. They can also run the VIN for you. I like this idea even more because you can have them tell you all the warrantied work and beyond that has been done to the vehicle. This is how I found out my window motor and fog light were the only things changed out under warranty before my purchasing the car. This data base also checks ALL OTHER GM service shops for repair work. Pretty cool, huh?
You'll know by tomorrow am. Just make the phone call.