Out of curiosity, I emailed the vendor. Here's his reply and one of my emails...
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Thanks for your interest in this vehicle. You are correct in that this Corvette was not a pace car used on the track (and our listing does not state that as well), but this is considered a pace car by the Indianapolis 500 due to its affiliation with the track.
We have contacted the collector and we will let you know what type of documentation is available on this vehicle. The party who owns this vehicle also owns franchised dealerships in Indianapolis and is a serious collector of these types of vehicle.
Thanks again for your interest.
Sincerely,
The V-Trade team...