You said

Next month's jam will be slightly different than our previous jams. We will be hosting our first Optical Optimize! This is a jam specifically for optimizing/improving/adding on to a game you already have submitted to the jam.

Does the original game have to have been submitted to the Optical Jam, or can it be a submission from any other jam?

It is encouraged that a previous Optical Jam submission is used for this, however, it is not required. Feel free to use any project of yours from anywhere that you may want to Optimize