Hmmm. Going through the list I count eleven that were aquired during my time working for Game Stop. I think it's sad that they don't sell GBA games with boxes and that most people trading games in don't care if you throw away the box, manual, code, etc. Even after telling people they could register the games and possibly get stuff, no one ever kept the box or papers. Call me a thief of a trash digger if you will, but I have no use for all those Pokemon videos and don't mind taking the codes out of the trash.
Also, a few of the things were either prizes from Nintendo, Nintendo Power, etc, or were gave to me. For example, Nintendo sent me a free copy of Brain Age and the Game Stop manager offered me the store display GBA micro after it's battery had died and the charger couldn't be found. I didn't take the micro, but got the code.
I also traded in a lot of the games I didn't like/want: all the Mario Party, Hamtaro, and Pokemon games (except for Emerald). Most of the games I bought new, but some of them I got used if they had a code sheet. Every used game I got had a working code. I guess most people that trade in games don't register them.