Daniel replies:

Thanks for the birthday wishes. There might have been more Mush books, but as has happened a number of times, the publisher bailed on the idea when the first book or two did not make a big enough profit. I always thought that profit was profit--you get back your investment, cover expenses, and you make money on top--but current business principles dictate that only obscene profits count. So a publisher will keep going back to the same author, because he makes them money--but insist on totally new projects in the hope that one of them will be another Captain Underpants. Not complaining--just explaining why no more Mushes.