User blog comment:Derax-Pagani/Chapter 507: Voice/@comment-4449950-20161026002708/@comment-3045936-20161027173206

Maybe he doesn't "know" every magic. But can command any magic in his  vicinity. His title is Mado'O which literal means Magic/Sorcery King. And what does a king do? He commands and rules. So he might know many types of Magic but not all. But can manipulate any that are being used close to him. Because last I check he used Slowing, Sound Magic and Reflector after each of the OS used it.