So I forgot to update here, but I did get a copy of Steel Diver the other day w/ a unused code. Not only that, when I told the guy at GS what I was buying it for, he pulled the point card out of another copy & gave me that one too - registered them both & that put me at exactly 700 points, so I redeemed for the poster set. I'm happy now.
So I went to GameStop and bought a "new" copy of Steel Diver for 3DS for $2.50 and tried to register the code. It was already used, so I took it back and ripped them a new one about their "new" games being used.
I was mistaken! The email didn't actually mention what was shipped. I went to the web site and apparently they shipped the Smash Bros. soundtrack!!!!