First an foremost, is a small modding community.
Treating your mod as a product to be marketed/sold is basically pointless.
Also realise that a vast majority of maps are being made with universes and storylines created solely by the modder, and not based on some pre-existing media. Stories that no one besides the creator knows about, and yet you don't see them asking if whether someone has heard of my story/universe or not being a problem.
That being said, if you're bothered by this then perhaps the problem is far more fundamental. After all, if youre that inspired by an idea that you'd want to make a mod based on it, why do care whether people have heard of it or not?