Bloody 'ell! That's rubbish! Well hopefully TGC will sort it for you and bully NVidia into giving you the right prizes. It's really not your responsibility, and while it sounds like it's NVidias fault for not sending you the right kit, it's definitely TGCs responsibility to chase it up.
I'd imagine whoever at NVidia is responsible for the compo prizes probably stuck it on the bottom of the todo list. Then when it finally finished they realised they hadn't pulled their finger out and done anything, so quickly rounded up a few boxes of kit and threw them at the postman. Very very lame.
In your shoes I would be very pissed off aswell and probably would've verbally ransacked several people on the phone and threatened to kill them.
Ok, perhaps not, but my blood would be boiling. It actually frustrates me a little just thinking about it now!
Definitely don't settle for the prizes you've got. With the amount of blood sweat and tears that goes into these compos, you deserve to get what you were promised, so keep at em until it's sorted. Let us know how you do.