Only one game is allowed per participant. This lets you take your time on improving your one game to the best of your ability. You can submit it early for others to play and provide feedback, then improve it based on that.
Games published before the start of the jam aren't allowed because the submission page would become full of spam and promotion. Hope you understand. But don't feel pressured to work on your game for a full month, you can make it the last 3 days of the jam and it'd still count. The jam is not competetive after all.