The cards themselves were included as Feelies for the Hearts of Stone DLC (Monsters and Scoia'Tael decks) and sold at CD Projekt booths during gaming conventions in Poland (Northerners and Nilfgaard decks).
Word of Saint Paul: It is generally accepted among the fandom that Korin from Road of no return was Geralt's biological father. However, it was not Sapkowski who came up with this idea, but rather Maciej Parowski, writer of the comic book adaptation.
Word of Dante: Since the author has a rather Shrug of God-style attitude, many world-building details were filled out by the fandom, the tabletop game, and finally the video games. The world map is probably the best example, as no map has ever been included in the novels. Even then it's just one of several versions circulating in the fandom.
Fan Translation: Made long before the series was fully published in English. Also the only way to read Droga, z której się nie wraca (Road of No Return) and Coś się kończy, coś się zaczyna (Something Ends, Something Begins) in English.
Disowned Adaptation: Zig-Zagged. Sapkowski stated that while he respectsCD Projekt RED's storytelling abilities, he does not consider the games to be canon. After the release of Wild Hunt, he became more hostile toward CD Projekt RED over their perceived mistreatment of the franchise, primarily over the Adaptation Displacement the games have caused to the original novels, regardless of reignited popularity of the books and their multilanguage translations. Sapkowski eventually hired a lawyer and attempted to sue CD Projekt Red in 2018 for having not received any money from their profits of the game series (despite selling them for a pocket change on his own without securing any further rights to any profits), as he had made a deal with CD Projekt Red when they created the first Witcher game. The case was dropped soon after, suggesting a back-room settlement.
Newbie Boom: Both the first and third games created a massive spike of popularity for the franchise, especially outside Poland and Czech Republic, while also reigniting and expanding fandom in those two countries. Wild Hunt in particular turned CDPR overnight into a major game studio, being a major success on all platforms and has been cited as one of the most influential open world role playing games of it's decade.
The Other Darrin: Except for Geralt, Vesemir and Eskel, every recurring character has been recast at least once during the trilogy.
Sleeper Hit: The first game was a PC-only single player CRPG released in 2007 by a newly formed development studio, backed by a publisher largely unknown outside eastern Europe, based off a fantasy setting almost unheard of in the English-speaking world. It proceeded to sell over a million copies in its first year of release. The success was such a surprise that the studio more or less apologized for their shoestring-budget hack job of a localization by using some of their windfall to produce a much more polished Updated Re-release with an expanded script and fully rerecorded voice acting.
There was a Witcher game in development from 1996-97 by Metropolis Software House, although it went nowhere and was unofficially cancelled. Interestingly, many of its supposed features (Geralt as the protagonist, dark and mature story, choice-based narrative) would be carried over into CD Projekt RED's Witcher games over a decade later.
The preview material for this project was the first time "Witcher" was used as an English translation of Wiedźmin, before the film went with "Hexer".
CD Projekt Red didn't initially plan to bring Geralt back to life in the first game. They originally intended to either have the player make their own Witcher character, or to have Berengar be the Player Character.
A remake of the first game for the Xbox 360 and Playstation 3 titled The Witcher: Rise of the White Wolf was announced in 2008. It was intended to have the same story as the PC Enhanced Edition, but feature a new engine and combat system more in line with the then-upcoming sequel The Witcher 2: Assassins of Kings. However, it was cancelled in 2009 due to disagreements between CD Projekt Red and co-developer Widescreen Games.