I've been happily using my US Nintendo Network ID until I had to move to Alberta, Canada recently. I tried changing the region from US (California) to Canada for my console and an error message popped up saying my Nintendo Network ID & the region doesn't match. Without much of a choice, since I had barely anything to lose on my account, I deleted my Nintendo Network ID completely and tried to make a new account with the same name but an Error Code: 102-2571 shows up saying that "The Nintendo Network ID you entered is already in use."
Now, I am convinced that someone wouldn't have taken the ID in a matter of few minutes because my ID is really weird and different that nobody would've taken it. Also, I thought I made a mistake on deleting the account so I tried to link an existing ID but another error message shows up saying "the account has been deleted."
So my question is basically, does it take time for Nintendo Network to recognize that my ID has been deleted and it is NOT already in use or has someone coincidentally registered my previous Nintendo Network ID Username after I deleted mine?
Sorry, I hate to be the bearer of bad news, no, it is not due to the Nintendo Network not recognizing that your deleted your Nintendo Network ID, or that someone was able to quickly register it, but as a way to try and help prevent gamesharing, a person can not log into another Wii U console with their NNID, so by deleting your NNID, that also removes any ties that your NNID had on your console.
So when you try to recreate the same NNID on your console, both the console and Network view it as trying to log onto another Wii U console and will automatically not allow that, sorry.
And unfortunately, other than creating a new NNID, there really isn't anything you can do, but give a call to Nintendo's 1-800-255-3700 (6 am ~ 7 pm Pacific, everyday) Customer Service number to find out if there is any way they can help you recover your NNID.