Piers Anthony's official bibliography lists a grand total of 29 Xanth books - not 70, not 40, but 29.
And the last two have release dates in the future.
Since book 8, he has written precisely one a year (with a single exception, #18 and #19 were both released in 1995.)
"Sometimes I Just Don't Understand Him" mode:
In his "Erotic Fantasy" line, he's apparently written the sequel to "Pornucopia", and, painfully enough, has decided to name it "The Magic Fart".
The guy *does* have a good imagination at times . . . as long as you keep him away from Xanth . . . and anything involving sex . . . though he'll figure out a way to work the sex in anyway.
But he still has had some good ideas :P