Might depend what they mean/meant by "serviced" Could just be a wash and wax and interior clen to make it look spiffy,It's not even due for it's first service so i don't know how GM could deny powertrain warranty. I would have that included on the bill of sale as well. Easy to pull GM warranty/service history with the vin. I would hope that a technician capable of working on Lambo's could change the oil in a Corvette. I also know that the odd GM dealer has screwed up an oil change on a dry sump system
And then check liquid levels. Don't see why they would change oils or anything.
Never the less it would be nice to know what it did in those first few K's