There was a reason Doc didn't WRITE the sequel to CotL; he apparently told it to Robert Heinlein, but HE never wrote it down. We can make some guesses, and there are some obvious events which happen that are implied in CotL, but we will never really know what Doc saw in the future of that universe. But some of those implied events simply couldn't have been PUBLISHED even in 1965 (when Doc died), and he was probably running quite a risk with the hints he put in.