When Is an Old Story a New Story?

Most novelists who have been writing for a while have an unpublished story or two that they haven’t given up on. You keep thinking that if you could just find the right twist or revise a character you can make it marketable. But how much do you have to change the manuscript to consider it a new story? Can you send a revised novel with a new name to the same editors and agents as though it were something fresh for them to read?

Or what about his scenario? You write a great sci-fi story called Death March into Armageddon. Publishers seem to like it, but no one offers you a contract. A few years later, you publish the story with a small press that goes out of business shortly after. Your novel only sells a few dozen copies. Five years later, you get a great idea for how to make the story better. You make those changes, spruce it up with a new name like Heavenly Invasion and submit it to a different publisher.

Can you consider this work to be “previously unpublished”? Is there a legal definition for how much a story has to change to be considered a new work? Do you have a moral or legal obligation to tell the new publisher about the manuscript’s history and the two dozen copies of the previous version that are still out there somewhere?

Has anyone been in this situation? How did you handle it?