maybe Tuvo is some kind of Mage who does exist in Middle Earth, and yet was not written of in the official canon of the Legendarium.....i mean, just like in the Bible where there are plenty of stories etc that don't figure into the official book, but were confirmed by later scholars as being deliberately left out of the Bible canon for political reasons, there could be entities etc that don't show in the written accounts of Elves or Hobbits that actually DO exist (and maybe they won't play a role in the first but rather the last Ages of Arda). all speculation
but remember Tolkien was a professor and would be used to the idea of several different readings/writings of events, both official and heretical...