That's strange that some items are marked as qualifying for the DLC when they don't actually qualify. Amazon needs to fix that. I had a hard time finding a game I wanted because I didn't want something that I could get on PC.

I purchased Shadow of the Colossus for $18.60, on the item page, it shows that it's elgible for the DLC, but the price is under $19.99, and I didn't receive a code.

I purchased another game, Persona 5 for $19.99 which met the minimum price requirement and a few hours later, I got an email with a DLC code. The email specified it was for Persona 5, so I know I didn't get a code for the other game.