There have been multiple games, mostly in the past now, that announced launching on certain platforms, including Steam, then had to backtrack and reveal that Epic bought their exclusivity and that gamers that were already expecting to get the game from one platform, now wouldn’t be able to.

There was one game that happened to. Metro. And anyone who had already pre-purchased on Steam had it fulfilled through Steam at launch.

The rest of the games people claim this happened to were Kickstarter projects in which the backer reward promised a “digital key”. Now, at the time of those Kickstarter campaigns, the only stores that existed were Steam and GOG, so there was an assumption made that the keys would be to one of those two. But by the time the games were getting ready to launch, another option came into existence and devs who clearly needed money (or they wouldn’t have been going to Kickstarter to begin with) made a deal.