Short answers, pulled from the story.
Wizards of the Coast released the first System Reference Document for Dungeons and Dragons third edition in the year 2000. This release occurred under the Open Game License and transformed the landscape of tabletop gaming by allowing independent publishers to legally build upon the core mechanics.
Wizards of the Coast abandoned the Open Game License in 2008 when releasing the fourth edition of Dungeons and Dragons. The company replaced it with the more restrictive Game System License, which resulted in a System Reference Document offering only lists of concepts and tables rather than the full text of the rules.
The full Dungeons and Dragons System Reference Document 5.1 was released under the CC-BY-4.0 license in January 2023. This Creative Commons license offered even more flexibility for creators following the update to version 5.1 by May of the same year.
The System Reference Document 5.2 was released on the 22nd of April 2025. This release continued the trend of openness and ensured that the community could continue to build upon the core mechanics of the game.
Publishers of games such as FATE, RuneQuest, Traveller, and Zweihänder Grim and Perilous RPG released their own System Reference Documents under distinct Open Game Licenses. These systems allowed their mechanics to be used by others in the same way that the Dungeons and Dragons System Reference Document had been.
Chase Carter of Polygon highlighted the evolving role of the System Reference Document in the indie game design scene in 2022. He noted that it had become more than just a technical tool and had transformed into a political statement about art and creation under capitalism.