My intention is to create a world in which my stories are written. The links that would exist between two stand alone stories would be setting and history. They might reference things that have happened in other books but would have no specific effect upon the plot. Forgotten Realms D&D setting is an example. They have many novels that have been published that reference lore but are written by a plethora of different novelists. When I sell the publishing rights to a publisher do I give up the rights to create more books that live inside that world until the advance is paid off? Would I need to continue working with the same publisher with permissions to create more stories within that world? Does copyright of the world I create eternally remain with me so that I am free to write in the world and publish with different companies with no repercussions?