Good question! The purpose of the assignment is to help you get your past year’s worth of photos organized and edited. However, if perhaps you have already accomplished that, here’s what I would suggest:
1st: Submit your best 12 from the past 12 months and submit them like normal for this assignment.
2nd: Prepare a second batch that could include photos from previous years and feel free to share (a link?) here on the forums, but not as an official submission. Those 12 would probably be what you would use in a calendar if your first batch won any prizes!
If you win a prize, you can use it to print any 12 photos you want.