Additionally, if i'm not mistaken, even the permit cannot be used beyond 30 days. However, many people use it for a much longer period.
Traffic officers should be educated further, but it is difficult, if not impossible, to verify a real permit as opposed to a counterfeit one since no States have immediate access to Korean or other foreign jurisdiction's driving privilege information.
Hope this clarifies. If you think I am wrong in anyway, I welcome any response as I would not want to disclose wrong info to the general public.