My 05C X77 (Made on May 15) has spoilers and no D80.
The D80 marking had to do with the arrival of Firebird Trans Am production to the Norwood plant that came there in mid May. The needed a way to keep the trunk lid apart from each other. Different holes for the spoilers
Here is some info on this topic:
http://www.camaros.org/forum/index.php?topic=3752.0