Originally Posted by Timlander
Still not the same as this was a promotion not a sale. You did not add that key with the whole-hearted intent on paying for the game. You got the key because you knew there was a mistake made and you wanted to take advantage of that mistake and get free merchandise.
A promotion is synonymous with a sale:
Part of Speech:noun
Definition:public notice of sale; notices to increase consumer desire
Synonyms:PR, announcement, announcing, ballyhoo, billing, blasting, broadcasting, buildup, displaying, exhibiting, exhibition, exposition, hard sell, hoopla*, hype*, pitch, plug, posting, proclamation, promo, promoting, promotion , publicity, puff, screamer, spread, squib
When someone adds the key to their purchase, they are purchasing it under the impression that it is a promotion/sale. Regardless of that, the fact remains that a contract was formed when the order was accepted and the goods were delivered. There are two ways of getting out of a contract: the Frustration doctrine (aka subsequent impossibility) and the Common Mistake (aka initial impossibility).
The Frustration doctrine only applies in situations where an unforeseen event makes the completion of a contract impossible or radically different to what it originally was, and only in a situation that isn't the fault of either party. Since the contract was completed, frustration cannot apply.
Common mistake - is when the contract was impossible from the beginning - for example, buying something that you already own, selling something that doesn't exist or has already been sold to someone else or a fundamental mistake as to quality. This doesn't apply here either since the keys were in existence and fully functional, and NVidia had the right to sell them. There's no mistake as to quality as the products are exactly what was being ordered.
Common mistake does apply to the customers who didn't get a key because NVidia ran out.
So there's no way for NVidia to back out of it here without breaking a contract, which is obviously illegal.