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Maybe I'm reading the question differently. The GMID & Supplier rate are the same thing. (This does NOT incude the employee pricing rate.) If you have been provided a GMID # from a GM employee than the dealer has the "option" of giving you that price on the Corvette. A "big time" local (former forum vendor) dealer laughed at me when I asked for the GMID rate. Another local dealer honored the GMID pricing, and so will (last I heard anyway) some of the forum dealers.
If you don't have a GMID # search the forum and/or ask. With Summer upon us I'm not sure how long they will be accepted but you can ask one of the dealers. (Les Sanford, Kerbeck)
But if your asking if the dealer will give you a GMID # or the discount without one, Nadda.
Sometimes dealers run specials and match those prices for anyone.
My brother paid less for his new 04 Z06 at the end of the model year than I did for a GMS priced 03 coupe. So it does happen. But it is not the same as giving you a GMS #.
GMID (which is both GM In the Driveway and Supplier pricing) and GMS are both based on 'certificate' numbers that are generated by GM. The dealer must then supply that number to GM when accepting it on a purchase. The dealer has the option of accepting GMID or GMS. Right now, GM has a special going on where anyone who is eligible for GM Supplier pricing can 'give away' 2 certificates (offer ends 5/31). Eligible GM employees can get a GMS certificate and can also 'give away' 2 GM in the Driveway (GMID) certificates.