Each Course has a number of attempts. Whenever you start a course you are doing the most recent version of the course. Also, if the course changes while you are doing the course, you are doing the changed course *immediately*.
So, "versions" isn't really accurate: if a course attempt is in-progress, you're always stuck on the latest version, whether you like it or not. It's not like you the student have the right to complete the course "as you started it".
This means if the number of quizzes increases, you need to do the new ones, etc. Now, if a course attempt is complete, then it's complete, and it doesn't matter whether the instructors increase or decrease the number of questions, quizzes, etc: your mark is your mark. (If you start a new course attempt, however, it's on the latest version of the course.)
So, to answer your question:
In terms of Course Sets, the way to think of a Course Set is just as a bundle of Courses + a certificate. So, the rules for an individual course still apply...