Shows spun off from it include:
Good Times (1974–1979)
The Jeffersons (1975–1985)
Checking In (1981)
Archie Bunker's Place (1979–1983)
704 Hauser (1994)
Happy Days, created by Garry Marshall, originally aired 1974–1984 and led to:
Law & Order: LA (2010–2011)
Law & Order: Criminal Intent (2001–2011)
Crime & Punishment (2002–2004)
Law & Order: Trial by Jury (2005–2006)
Paris enquêtes criminelles (2007–2008) (French adaptation of Law & Order: Criminal Intent)
Закон и порядок: Преступный умысел (2007–present) (Russian adaptation of Law & Order: Criminal Intent)
Закон и Порядок: Отдел Оперативных Расследований (2007–present) (Russian adaptation of Law & Order: Special Victims Unit)
Law & Order: UK (2009–present)
Law & Order: Cape Town
So, what does this have to do with books?
Lots of books are parts of a series, including the well-known James Bond and Harry Potter dynasties.
But even books that are not parts of a fictional series can spin off other books.
My Become a Real Self Publisher was first published in 2009. It has led to at least SEVENTEEN spinoffs, and I'm not through spinning yet.
My first self-pubbed book was I Only Flunk My Brightest Students, published in 2008. It has led to at least six spinoffs.
Spinoffs have been an important part of authoring since the beginning. Homer did it, Shakespeare did it. The New Testament was a spinoff of the Old Testament.
The words you've already written are some of your greatest assets. Look them over. Think about how you can modify them, repackage them, update them -- and make more money.
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After I uploaded this I discovered that Forbes recently published New Year's Resolutions for the Book Publishing Industry. The first one is "publishers should resolve to find new ways to develop more of the intellectual property they own." Forbes is right.