I wonder why Wisconsin went through the trouble vs some incrementing id. It seems like it was understood 2 people could end up with the same number so the last two digits were added. That would rule out the benefit of unique ids without requiring a single central system to ensure uniqueness.

It does make it harder to fake an id, perhaps that was the motivation.

Edit: Some more interesting info for the states that implement this. Also, TIL Illinois drivers can appear to have the exact same DL number. http://www.highprogrammer.com/alan/numbers/dl_us_shared.html