It sounds very odd, it'd be like having a "Toyota By Design" plate on a Lexus. I've never seen any such plates on a HSV before when major options were added. Not saying it didn't happen, just it'd be weird. You'd think the HSV plate would point to their records, which would document what options were fitted. As far as i'm aware the HBD plate is so it is known (probably for warranty purposes) that the particular vehicle was fitted with HBD accessories as Holden's own records normally wouldn't record this as they were more often than not done post vehicle completion.