The article described Iron Mountain as the "keepers of GM corporate records. If they are a shredding company, it sure might explain why you have no records of the old cars in the US. I hope this is not the case.

I just did a Google search. You may be right although they store stuff too.
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Chevelleless after 46 years......but we did find a low mileage, six speed, silver 2005 Corvette. It will just have to do for now.