My father has a story he likes to tell of when he did testing for a game company. This was before videogames were mainstream, so he was doing test runs of an old school RPG. I won’t give away too much about what game, but it has a lot to do with running and shadows. He had been game mastering a campaign with the system, and one of his supervisors came in to check on him. So, my dad starts talking about the campaign, particularly an NPC called the Paladin. The Paladin was an actor that wore a suit of “armor” that was actually a bunch of recording devices. The devices existed already in the game, but the supervisor said they wouldn’t fit into the suit. My dad continued the campaign, and finished his testing.
A year or so later, he sees a module for the game that uses the Paladin, relabeled as Knight, as well as several other ideas he had. He was not credited anywhere, and had done the testing for free. That night, my dad sat down with his game buddies and decided that if his ideas were good enough to be published, he would publish them in his own system.