The keys are referred to in a book for children, The Voyage of the Poppykettle (and later The Poppykettle Papers), by Robert Ingpen.
The Pickwick Papers | Pentagon Papers | Federalist Papers | We All Had Doctors' Papers | The Pickwick Papers (film) | The Valachi Papers | Research Papers in Economics | Palestine Papers | What the Papers Say | The Valachi Papers (book) | The Poppykettle Papers | The Pickwick Papers (TV series) | The Pickwick Papers (TV series) | The Pickwick Papers (1985 television series) | The Pickwick Papers (1952 film) | The Pickwick Papers | The Pertwillaby Papers | The Aspern Papers | Nationalities Papers | Fraser Papers | Federalist papers | Cinema Papers | Bambu rolling papers | Annus Mirabilis papers | A Manual for Writers of Research Papers, Theses, and Dissertations |