Well we (CICC) posted the schedule that was on this site on our site July 8th and the car show was listed. The show details and classes were posted July 23rd
HERE in the thread linked. So there was some advance notice. I believe it was also in the schedule listed in the C5Fest III booklet in your blue bag.
They did announce very early on Friday and later on the PA that car show registration was at the Chevrolet tent so I immediately went over and let Scott know that if anyone asked about car show registration we were doing it at our tent next door, Scott then relayed this to all the Chevrolet people there. He did say someone had asked but he didn't know what to tell him at the time.
In hindsight we should have had a "Car Show Registration" sign out front of our table, heck I think we may even have one somewhere DOHHH!!!! (Leftover from Indy08) For that I do apologize.