One person, one story:
It hasn't been in the rules but I think one person, one story is ideal. Two persons, one story may work. One person, two or more stories is a bit much.
I think it is mostly bad for the one who submits several stories. It's similar to having another account. If they'd use both frequently it would take them much longer to reach the next rank and to get a decent amount of likes, because they'd have to divide the total amount of posts written and likes got by two.
Same goes for the contest. I'm certain that neither story has a chance to win, because the limited amount of votes get spread about one story more, reducing the average amount of votes every story gets. And most people who realize that two stories are from one person won't vote for both of them.
The writing contest is to hone your skill in writing and I think a part of that is deciding if a story is worth or not and if not to improve it until it is or discard it and write another. If everybody would submit as many stories as they liked, the quality would drop a lot and nobody would read them anymore.
Everybody should submit one story and let it be the best they can come up with. And if three drafts fall by the wayside, their story has already won its first contest and is ready for the next.
