Hey Rebecca,
Certifications are for the same courses - the grades are historised and reset. But from your description it sounds - a progressive pathway - like new courses on a continuum of learning? Maybe a program would be better suited. For the minimum required pass you could set a passing grade for the whole course - and have a suitably grading scheme for the various quizzes within it such that learners have to pass 4.
Please let us know if you have any further questions.
cheers,
George.