Get User Rank
This is a slightly-useless tool that uses internal NNID server variables to determine how many NNIDs have been made before yours.
To use this, just type any NNID into this box, and my server will automatically convert it to a ranking for you.
This uses Principal IDs, an internal number counting down from 1,800,000,000 that is given to every NNID by the server, and works on deleted NNIDs as well as verified ones.
This number may or may not be exact, I don't know everything about how Nintendo's internal servers work.

Also, in case you're wondering, the first NNID ever made was "prodtest1", made by a Nintendo employee at least 15 days before release. The More You Know™