I purchased a GMC which also qualifies. The dealer did in fact have the authorization number and at first put it through, while I watched. That's when he checked with his mgr because he didn't know how to handle the paperwork with the earnings, and came back and said they wouldn't accept the earnings. We did have them reverse the earnings at that point beacuse we didn't want the dealer to get the money from GM and keep it for themselves. All the earnings on my card would qualify for this purchase.
I really don't know if it's an issue of the dealer having to wait for the money from GM or that they could've gotten more money for the purchase if they knew I had the card. It's hard to know what they were thinking at that moment, but after the purchase price was agreed upon I did mention I had earnings.
My biggest frustration is GM earnings authorized it, with my information and the vehicle VIN number, and every requirement was met.