50 Years of Terry

50 Years of Terry was announced as a year long celebration of Terry Pratchett, timed to begin on the 50th anniversary of the publication of his first novel, The Carpet People. It was mainly visible in the release of new paperback and audiobook editions of the Discworld novels, with new matching cover designs cover art designed by Leo Nickolls, referencing Paul Kidby's character designs, and published for the first time under the Penguin imprint. Penguin stated that the new paperbacks would not replace the current 2012-213 paperback editions, which use modified versions of Josh Kirby's covers.

Harper Perennial

In April 2024, Harper Perennial announced similar paperback editions - using the same covers - would follow in the US, beginning with the Wizards series that month. This was linked to Forty Years of Discworld celebrations. (harpercollins.com)

Timeline

This includes all publications explicitly announced to be part of the celebration, as well as those that happen within the period. These are based on announced publication dates, which are primarily for the UK (though audiobook dates are usually international). Some regions (e.g. Australia) will see the new paperbacks a few months later, and separate Harper Perennial editions will be published beginning in 2024. Many of these dates have been subject to change, and the celebration ended up extending beyond the officially announced year.

16 November 2021: New audiobooks announced.
9 December 2021: Hogfather audiobook, narrated by Sian Clifford, with the same cover art as the 25th Anniversary edition of the book released on 15 October 2021.
1 March 2022: New paperback editions announced.
22 April 2022: Official start of 50 Years of Terry. Publication of new 50th anniversary edition of The Carpet People, and new audiobook read by David Tennant.
28 April 2022: Publication of new paperback editions of the Witches books Equal Rites, Wyrd Sisters, Witches Abroad, Lords and Ladies, Maskerade and Carpe Jugulum, with matching audiobooks read by Indira Varma, as well as a new paperback of Small Gods with a matching audiobook read by Andy Serkis.
7 July 2022: New audiobook editions of the Wizards books The Colour of Magic, The Light Fantastic, Sourcery, Eric, Interesting Times, The Last Continent and Unseen Academicals, read by Colin Morgan, with matching paperback editions for every book except Eric.
1st September 2022: Publication of Special Edition paperback of The Amazing Maurice and his Educated Rodents, featuring new illustrations by Laura Ellen Anderson and the story of how Terry came up with the idea, written by Rob Wilkins. Uses a version of the cover art from the 2018 Corgi edition.
29 September 2022: Publication of Terry Pratchett: A Life with Footnotes by Rob Wilkins, and the film tie-in edition of The Amazing Maurice and his Educated Rodents, with a cover using the logo and Maurice design from the film.
5 October 2022: Publication of new audiobook edition of The Amazing Maurice and his Educated Rodents narrated by Ariyon Bakare (who plays Darktan in the film version). It has a cover matching the design of the other new editions, but it's not clear when (or if) there will be a matching paperback.
27 October 2022: Publication of new paperback editions of the Death books Mort, Reaper Man, Soul Music, Hogfather and Thief of Time, with matching audiobooks read by Sian Clifford, including a reissue of the Hogfather audiobook with a matching cover.
3 November 2022: Publication of new edition of The Unadulterated Cat to tie-in with The Amazing Maurice film, with the title changed to the The Unadulterated Maurice and a new introduction by Rhianna Pratchett.
23 February 2023: Publication of new paperback editions of the standalone books Pyramids, Moving Pictures, The Truth and Monstrous Regiment, plus matching audiobooks of The Truth (read by Mathew Baynton) and Monstrous Regiment (read by Katherine Parkinson); and new editions of the Moist von Lipwig books Going Postal, Making Money and Raising Steam, with matching audiobooks read by Richard Coyle, reprising his role as Moist von Lipwig from Going Postal). In addition, Gollancz publishes a new paperback edition of Eric with a cover matching the new Penguin Rincewind books.
30 March 2023: New audiobook of Pyramids read by Alfred Enoch.
18 May 2023: Publication of new paperback edition of Moving Pictures, with matching audiobook read by Jason Isaacs.
25 May 2023: Publication of new paperback editions of the Watch books Guards! Guards!, Men at Arms, Feet of Clay, Jingo, The Fifth Elephant, Night Watch, Thud! and Snuff, with matching audiobook editions read by Jon Culshaw.
15 June 2023: Release of new audiobook editions of the Tiffany Aching books The Wee Free Men, A Hat Full of Sky, Wintersmith, I Shall Wear Midnight and The Shepherd's Crown, read by Indira Varma with Steven Cree as the Nac Mac Feegle.
7 December 2023: Publication of new paperback editions of the Tiffany Aching books The Wee Free Men, A Hat Full of Sky, Wintersmith, I Shall Wear Midnight and The Shepherd's Crown.
29 February 2024: Publication by Gollancz of a new paperback edition of The Last Hero, featuring a cover matching Penguin’s new designs.