I would just think of the basics of what a sequel is: "the book/movie/etc. that happens afterward". 

From there, you can use the words tey (tale), se (of), and after (mindin) in the word-of-word construction (in the lessons) to formulate the meaning you want:

teysemindin (tale of after)

From that logic, a prequel could be conveyed as teyseus (tale of before).