Branching quiz based on unanswered questions

I'm using Captivate 5.5 to design an awareness module that contains 2 short knowledge checks at key points in the module (around 5-6 questions for each). The knowledge checks aren't compulsory and learners can move freely backwards and forwards through the module, and therefore can skip questions.

We want to encourage them to answer all the questions (but not force them to if they don't want to). I've thought of branching the module at the end, with uncompleted questions branching to a reminder slide, and all questions completed going to a summary of the module.

The way I've tried to do this is to use an Advanced Action with the CpQuizInfoTotalUnansweredQuestions variable to trigger the branching. This works okay if the learner doesn't move backwards. Once they go backwards past a question they haven't answered yet it will be counted as unanswered a second time. This means that there is no way they can ever get the variable to 0 and then move to the summary slide.

Is there any way to use the CpQuizInfoTotalUnansweredQuestions variable to get it counting the unanswered questions correctly?

The other way I had thought of doing it was to add another variable that changes when the branching/reminder slide is visited the first time, and having the Advanced Action check the variable to see if the slide has been visited before and if it has then it forces the slide to be skipped. This would assume that the learner went back and found and answered all the questions they missed or decided not to answer them all.

Thanks in advance for any help or suggestions.