Tolkien did make some well known mistakes, and when he found them he tried to find explanations for them and make them fit into his legendarium. One example is Glorfindel. He created the character for Lord of the Rings, and yet there was another Glorfindel in the Silmarillion - in Gondolin. He tried to explain this by saying that Glorfindel of Gondolin went to the Halls of Mandos and was later exceptionally allowed to re-enter Middle-earth.
I actually like the fact that he made mistakes and attempted to explain them. It makes his secondary world all the more real; there are contradictory theories and seeming intellectual mistakes in the real world. Tolkien also deliberately left some things unexplained or unexplored; that his world has 'fuzzy edges' again makes it more believable. Though I have to wonder if his wish to have these fuzzy edges was not just a way of accepting that as a perfectionist, he would never fully complete his world?
I love chewing the various issues over though. Just as we think we have one idea defined, someone comes along with a new mad theory and the old debates start off all over again. That's what it's all about...being a Tolkien nut I mean.
