Idk where to draw the line with it being illegal for them to sell real copies. Like, what if it’s a really good fake? Are they gonna send out each and every game? They can’t spend $20 making sure a $10 game is legit.
No clue what to do about it honestly
Seconding OpenCourseWare. I used that a lot before and during undergrad (engineer with math minor).
I do recommend checking out the “fun” math videos as well because you’ll learn a lot and it’s fun, like Numberphile, 3 blue 1 brown, etc