I don't even see the core DLC as an option. My Library just says "Offworld Trading Company" (though it's just the Multiplayer Client) and the store says "Offworld Trading Company" on the main store page - no mention of being the *core DLC*. And while Steam is recognizing both as being the same thing (since they're apparently listed as the same thing) ... they clearly aren't, as the GAME is still locking me out of single player options.
I did just get this response from Stardock's Facebook page:
"This appears to be an issue on Steam's end, so our publishing director has reached out to Valve to get it corrected. I'll let you know as soon as we hear anything. Thanks so much for bringing this to our attention, and have an awesome day!"