Oh, there were 11 Mars books (a couple were collections of short stories or novelets, and there were three Conan books that were 100% Howard. de Camp and Carter began the only Cionan industry and adapted many of REH's unpiublished stories into Conan and then wrote originals. They weren't anty good; neither were the other pastiches for the simple reason that the author needs to be totally bugfuck mad. Howard certainly was!

I love de Camp's other writings; I forgot that he dealt with Oz in the Compleat enchanter series though!

For information on Shanower's Oz books and the Oz annual, see http://www.hungrytigerpress.com/books/adventuresinoz.shtml