How do I find the latest completion date when working with a bunch of completion dates that are stacked up with no deliniation between?

Good Morning,

I am wrestling with an issue and need some input on how to solve it.

The data that I am working with is training data, therefore there is a student name, course name, due date and completion date. Pretty standard stuff.

What is confusing me and is the crux of the issue that I cannot differentiate one completion date from another completion date. 

What I mean by this is that completion dates just stack up on top of each other with no mechanism or a fiscal year date to differentiate one from another.

Ideally, I think you would have a situation like this

Another issue that I think that is compounding my problem is that some of the courses that I am working with have a business rule set so the next due date is assigned 365 days after the last completion date.  What I mean by this is this:

I think it is important to note that in my real life the due date are in one table and the completion dates are kept in another. The due date information does not have a history meaning only the latest due date for a student and course are kept as compared to the completion dates which does have a historical aspect to the data.

So in my reality when I join the due date table to the completion table the data looks like this:

The completion status is a product of a calculation that I built.

I don't know if solving this problem is best done via Prep or Desktop but looking for ideas and input as to how to approach this.