I recently had questions about how wise it would be for me to try to sell some short stories to magazines set in the same universe as my novel while I am waiting to hear back from agents whom I've queried my novel to. The idea was to do a bit of world building in other publication forums while trying to get the novel published.
My concern was that I would anger an agent or publisher who might have been considering representing me and my debut book and/or publishing it -- by having pieces of that fictional universe the book is set in already owned by another entity (in my case, a science fiction magazine).
I knew better than to use the same characters and places from the novel. But I wasn't sure if I could use character names only mentioned (or with bit roles) and/or characters never seen in the novel. I also wasn't sure if I could explore different timelines in the universe that aren't shown in the novel.
So I asked around, and I got feedback from two literary agents. Here is what they told me:
"First of all, NO publishing company owns your IP here. It's yours, all yours. Only if you had created something they dreamed up (Star Wars, Star Trek, etc) is it considered Work For Hire. When you submit a novel for consideration, having published short stories is a good thing. It shows there's an audience for this."
"In my experience it's not a bad idea at all. In fact, a short story gone viral can be increase your chances for a book deal. Good luck!"
So there you have it. Two different literary agents have told me that it's okay to sell short stories set in the same universe as the novel you're querying. Just don't use the same characters from the novel, and there shouldn't be a rights conflict.