I think it would probably count as a brainstorming session. I also don't see how you have a game where the two main players are on different orbital bodies, one of them solving a mystery and the others having a space opera/survival adventure. Basically, I can't see how the events of even Leviathan Wakes can be reverse engineered into the events of a tabletop game. Maybe the Canterbury-Doniger-Rocinante plotline, but I don't see how you would have worked Miller into it.
Also, the "bulk of the content that became The Expanse" is a lot of people reacting to the weird shit that Protogen or Laconia is up to, and discovering new and horrifying things about the protomolecule and its subsequent iterations, like the gates, and the ring space and the other worlds, and then the dutchman phenomenon. I would also bet that the Inaros faction of the OPA was the DM-guided villains. What I mean is, it looks like most of the content was written by whoever made up the games and the adventures. I have been operating on the assumption that this was primarily Franck and/or Abraham. As I understand it, the guys who are just playing would not have invented the protomolecule or the Epstein drive. Were Winston Duarte or Anderson Dawes or Crisjen Avrasarala or Klaes Ashford played by characters, or was that the work of the guy who ran the games?
To put it another way, what if the WoT RPG was entirely the work of Robert Jordan, before he wrote the books. He creates the One Power, the Dark One, the Shadowspawn, the Ogier, the geography, the nations, the concept of a wolfbrother or a sniffer, the Heroes of the Horn, ter'angreal, and so on. Then he sits down with his young friends, Randall, Perry, Mathew, Gwen and Nancy (their friend Elaine missed the first few sessions and joined up later) and they make up characters and start at level one and begin playing.
"Randall, you are walking down a road with your dad. Suddenly you see a man in a black cloak on a horse, staring at you and you feel like he hates you. What do you do?"
"I shoot him with my bow."
"Okay, we're rolling your mental put-together-ness and, nope, you are too out of sorts to nock an arrow, let alone shoot. You trip as a result. Your dad notices. What do you tell him?"
"I tell him about the rider."
"He looks in the direction you indicated, but the rider is gone. He gives you a look like you've gotten into the brandy on that cart already."
"I try to look for some clue or think of something I might have noticed that might help me understand WTF is going on."
"I am rolling for your Noticing Things skill, and you ... pass! You don't see any trace of the rider or his horse, but you remember that despite the strong wind which feels like it came all the way down from the nearby mountains without being the beginning, but being a beginning, the rider's cloak did not move, even though you and your dad are having to hold onto your own."
"I don't bother mentioning this to dad. Maybe it will cause an ambush or something to happen that will get me treasure and more levels."
Now if someone decides to make that the first chapter of a book, who gets the creative credit? Robert for coming up with everything, or Randall, for making those choices for his character?
(Feel free to correct me if that is not how RPG work. I read, but never actually played, the WoT game. Several of my siblings tried to play it once and gave poor reviews. Nor have I ever played any other tabletop RPG. I did play the board game HeroQuest as a kid, but that's as far as my experience goes, despite extensive reading in the Dragonlance, Forgotten Realms & Warhammer 40K settings. That one session by brothers & sister attempted is the grand total of all RPG experience in my generation of the family. What I do know of the conduct of RPG is gleaned from scenes of people playing such games in films & TV shows and the opening chapters of "The Sleeping Dragon" by Joel Rosenberg)
So the question, I suppose, is what role did Franck & Abraham play in the game? If they were the guys running it, I rather think they are entitled to the overwhelming bulk of the credit and compensation. Not to mention, the very act of adapting a lot of gameplay into a narrative with coherent characterization is an amazing amount of work. And we don't know if there actually was some kind of compensation involved for the other players. For that matter, why publish it under James S. A. Corey, instead of their actual names? They use their own names for the production credits on the show. I think the pseudonym might be a joint thing, like the registered corporation that legally owns a business, and maybe the other players are part of it, and entitled to an agreed-upon share of the proceeds. That's pure speculation on my part, but it's based on the fact that we have heard exactly nothing about any sort of controversy based on the ownership of the IP.
Given the success of all the books and the TV show, you'd think one of their collaborators would have made a complaint about their due share by now. Even if there was a verbal or handshake agreement that if Dan & Ty can actually sell a novel based on their game, they can keep all the income, when you get up to TV money, it kind of defies any understanding of human nature, that no one in the group maybe had a casual conversation with an attorney as to just how binding that handshake was, and whether an attorney's percentage of even a minimal settlement might not be worth filing some court papers alleging IP theft. What that says to me, is one of several alternatives:
A. Abraham & Franck have a VERY generous group of friends who really are okay with the duo getting all the rewards of their creation
B. The contributions were insignificant or irrelevant to the actual composition of the story under any legal standard applied to intellectual property, meaning that the authors wrote so much or changed so much from the game that what the others did was negligible. Meaning that their acknowledgement of the other players is actually Abraham & Franck being the generous ones.
C. They are sharing the proceeds with the other players, in a division that is satisfactory to all parties involved.