ThreadSteam "leak" - EULAs uploaded for unknown SteamApps including EA Games, Dragon Quest Rivals etc.
These are EULAs that developers put in Steamworks (any dev with an app can add an eula, so you can write anything there).
With that list, there's some titles like generic "EULA" or "Terms of service" but the actual text may contain name/developer, so if anyone's bored enough — go through them, will probably find a few more upcoming games.
ThreadPC Gaming Era | March 2019 - The Ides of Smarch
Someone entered a key for that, but it was already used, it still grabbed the name though.
So if you have keys for stuff that doesn't have a package name on SteamDB, you can submit a used key and it will be able to grab the package name.