Lin Carter worked with L. Sprague De Camp to fill in the Conan timeline based on the notes that Robert E. Howard had left(Howard committed suicide).
There are over 100 Conan stories now, I think, though only about a dozen are Howard's original works, with another dozen by Carter and De Camp which are based on his notes.
The rest are done by generic fantasy writers, and a few other big names, like Robert Jordan (who has written five Conan books, I believe). It's kinda like the litmus test for fantasy writers: if you can write a D&D or Conan novel, you can move on to other things.