As a longtime fan of Terry Pratchett's Discworld series, I can confidently say that the talking books do cover a vast majority of the novels, but not every single one. The entire series spans over 40 books, and while most of the popular ones like 'Guards! Guards!', 'Mort', and 'Going Postal' have been adapted into audiobooks with fantastic narrators like Stephen Briggs and Nigel Planer, some of the more obscure titles might not be available in this format yet.
The earlier books, especially those from the 1980s, took a while to get audio adaptations, but the later releases were often simultaneous with the print editions. If you're looking for a specific title, it's worth checking platforms like Audible or your local library's digital collection. The narrators truly bring Pratchett's wit and humor to life, making the listening experience just as enjoyable as reading.