yes, design docs or notes are ok. Just no code or art made specifically for the project.
But the rule says
- You CAN use external libraries, game engines, pre-existing code/algorithms, pre-existing art, etc. You can even start your game from an existing game, if you are planning to turn it into something unique. If in doubt, be clear what resources were reused.
If I want to make a roguelike platformer, and I coded a non-roguelike platformer before.
Is it valid to use the previous game's code?