Just a word of caution so no one has the hassles I just did.
I created a Club Nintendo account a year or so ago when I got my oldest boy his 3DS and have been adding purchases to it ever since (including a Wii, WiiU Deluxe and another 3DS I got for my other son for his birthday next month).
Anyway - I bought myself a Gold Zelda 3DS XL (so now a 3rd DS system) and figured I'd do the free Pokemon X or Y offer so I linked it with my WiiU Nintendo ID - worked fine.
I then went into my Club Nintendo account and registered it - again it worked fine.
I then went to register my newly purchased Mario Kart 7 to qualify for the offer - and it would not register. So I called Nintendo.
The very nice guy there tried to register it for me - but it would not work. Turns out - my oldest son's copy of Mario Kart 7 I registered a year ago was keeping me from registering the newly purchased 2nd copy I just bought yesterday.
He has to now escalate this to someone else - after having me create another "user" on my Club Nintendo account so I could actually register this 2nd copy of Mario Kart 7.
He said it would take up to 10 days for them to review it decide whether or not to approve the free Pokemon offer for me. If they don't approve it - I'm going to be pretty unhappy with Nintendo. Not counting all the various games for the 3DS and Wii and WiiU - I have (2) 3DS's, one 3DS XL a Wii and a WiiU Deluxe registered. It's not my fault their system won't allow the registration of 2 copies of the same game under the Club Nintendo account - I'd think this is something they should have accounted for when they created the list of the approved games needed to get the offer.
In his defense he said he "suspects" they'll approve the offer - but just wanted to caution me that there's a chance they may deny it. I will be calling back and raising heck if they don't.