I've never quite understood the idea of adding a game scenario to a fictional timeline. After all, each version of the game is going to be a somewhat different sequence of events happening to a different set of player characters. There isn't even a single fixed outcome, unless the game really "railroads" the players and limits their choices (which is something I've been trying not to do in my own scenarios). So there's no one version that counts as what "really" happened.
For sure, although some universes, such as
Star Wars, count gaming scenarios as part of the timeline with "default" Light Side endings (in most cases), even with drastically-different Dark Side outcomes (such as with the
Knights of the Old Republic series, which can end with the entire Republic getting conquered, for instance).
Also, for many gaming franchises where player choice offers vastly-divergent endgame outcomes (such as
Mass Effect, Fallout, The Witcher, etc.), you kind of pretty much have to have at least one designated "canonical" ending, especially for timeline-keeping purposes and developing the
next game in the franchise (for example, did Commander Shepard cause a planetary genocide in one game, and how does that affect the universe in the next game, or did the player choose the opposite action, and which of those two choices should be "counted"? Or, did Geralt allow Prince Stennis to be killed, clearing the way for Saskia to take over the entire Pontar region, and if Andrzej Sapkowski writes any future novels, does he use this particular ending, or the one where King Henselt survives the peace conference?).
In properties like
Mass Effect and
Dragon Age, where the games pretty much drive the franchise and the tie-ins are built around them, it's the games that possess branching storyline-outcomes which have to have a developer/writer's room-decision on which ones carry over into the "default" timeline of the universe, and which ones do not.
The Witcher is a very unique case in that the franchise began with a number of prose works, and then the video games are the official, author-endorsed continuation of the books (and are arguably globally better-known than the books, as well).
In franchises like
Star Trek, you don't necessarily have to have a default "light-side"-type ending for RPG adventures, but I still count the
overall events as having happened (usually taken from a logline in a sourcebook, or from the exterior cover of the adventure-module), but I simply don't specify what the final outcome is in my notes. For example, here's my entry for the Modiphius RPG module
Away Team: Signals:
A Galaxy-class starship investigates the disappearance of the runabout U.S.S. Susquehanna in the Carina Nebula, deep within the Shackleton Expanse.
I list the catalyst-events, but shy away from specifying a final outcome to the storyline (based on varying player-decisions that may occur during the course of the adventure).