I believe FCs aren't actually tied totally to discs. I'll find the link in a second, but I believe this is how it is.
Your Wii has a standard friendcode. (That's your friendcode)
You disc has a friendcode (that's not the one you see in the game)
For security reasons, there are some mathematics done here, that make up a new friendcode which is the one you see in the game.
Now this is a problem for me, as I bought a Wii for 1/3 of the price, because the FC on the Wii was broken. Therefore I can't get friendcodes for my games.
http://www.vgchartz.com/games/userreviewdisp.php?id=261
That is VGChartz LONGEST review. And it's NOT Cute Kitten DS







