Hi PhilipFX, as discussed...
About the Slug system,
I can modify this part to work as you need with,
1. Add some dropdown/checkbox elements to select the parent Lesson Level and the Lessons you need to attach to each Product/Download.
2. Write the User Purchase details in DB.
For this task, i believe it's ok to use the purchase info from EDD and from there we can find the Lessons associated with each purchase.
3. Modify the Lesson Purchased checks to work with the new Product to Lessons Attachment functionality.