Many mystery writers have a prequel as the final book in their series, usually dealing with the detective's first case, how they became a detective. Sometimes these are written many years after the other novels about that detective. Why do the authors choose to do this? Is this a way for the publishers to get the authors to write one more book--appealing to an author's desire to do something different with a character they might feel they've done everything with they could?
Examples: H.R.F. Keating (Inspector Ghote series), Gillian Linscott (Nell Bray), Leonard Tourney (the Elizabethan amateur sleuths Matthew and Joan Stock).