According to an interview, the novel started out as a story for a MMO game project that got cancelled early on. Part of the plot then got repurposed into a homebrew tabletop RPG for a gaming group, and THAT resulted in someone telling the authors that they really should write this down.
The original outline for the novels included three books that would have filled the thirty-year gap between Babylon's Ashes and Persepolis Rising. The authors eventually cut them in favor of a Time Skip, although they ended up releasing a novella (Strange Dogs) set in this period.
TV series
Actor Leaves, Character Dies: In the fifth season finale, Alex dies of a stroke with little buildup because Cas Anvar had been fired for sexual misconduct and the show needed to provide an explanation for why the character wouldn't be in season 6.
Ascended Fanon: An interesting example. Shortly before the third season began airing, the show's crew commissioned and worked with YouTuber Spacedock (an admitted fan of both the show and books) to produce a series of videos fleshing out the ships seen in the show. As there's not as much detail about them as there are with ships from other franchises, Spacedock did have to devise some things from scratch. Most notable is a consistent scheme for how components are named by the UN and MCR.
For the entirety of Seasons 1 and 2, Florence Faivre's name has a fixed spot quite early in the intro despite Julie Mao having significantly less screentime than most of the actors that get billed after her. She retains her spot even in episodes she doesn't appear in, but more importantly for the whole of Season 2 despite not appearing there at all. Then she doesn't receive any billing in Season 3 whatsoever despite making a couple of flashback appearances.
Cara Gee (Camina Drummer) was consistently billed as a guest star despite playing a major supporting character from Season 2 onward.
Shohreh Aghdashloo never loses her And Starring billing despite Chrisjen Avasarala making next to no appearances in the second half of Season 3.
Dyeing for Your Art: Thomas Jane lost a lot of weight and with it most of his hunky appearance to reflect that in Ceres' lower gravity people stretch out and become lanky.
Executive Meddling: SyFy put pressure on the producers to ignore the books and audition anyone, in regards to race, for the part of Bobbie Draper. To be fair, the description in the novels—a 6' 6" 220 pound Polynesian woman—was hard to live up to. Fortunately the producers ended up finding 5' 11" Frankie Adams, a Kiwi actress who was exactly who they needed.
Genius Loci. The series shows the effects of vacuum, zero gravity, and thrust gravity so well because the writer's room treated Space as its own character. They would ask, "What is Space doing during this scene?"
Hide Your Pregnancy: Cara Gee was pregnant during the filming of season 5, so Drummer is seldom shown below the shoulders during that season.
Only So Many Canadian Actors: The main parts are played by a variety of nationalities, but most of the smaller roles are filled by Canadian actors thanks to the shooting location.
The Other Darrin: As a consequence of the series' season 3 cancellation and subsequent renewal, Arjun's original actor Brian George was replaced by Michael Benyaer, as the former had moved on to other work in the meantime.
Promoted Fanboy: Amazon owner Jeff Bezos is a big fan of the books and was reportedly "livid" when SyFy outbid him for the rights to the series. He got the chance to save the show after the latter canceled it.
Real-Life Relative: Twin siblings Emma and Ian Ho played fictional siblings Cara and Xan in Season 6.
Role-Ending Misdemeanor: Cas Anvar (Alex Kamal) was fired after Season Five following multiple allegations of sexual misconduct.
Self-Adaptation: Daniel Abraham and Ty Franck, the authors of the original source material that this series is based off of, serve as screenwriters for the show.
Sending Stuff to Save the Show: After the show's cancellation, fans of the show flew a banner with the words "SAVE THE EXPANSE" on it in front of Amazon Studios. They got their wish.
Separated-at-Birth Casting: Jasai Chase Owens (Filip Inaros) shares enough features with both his on-screen parents Keon Alexander and Dominique Tipper that he's very believable as their son.
Screwed by the Network: Digital distribution rights were a key factor in the show's cancellation.
, the novel started out as a story for a MMO game project that got cancelled early on. Part of the plot then got repurposed into a homebrew tabletop RPG for a gaming group, and THAT resulted in someone telling the authors that they really should write this down.