Thank you for your help.
We do use autobinding and so technically we do save their progress pre-exiting the browser, and I also thought about the URL parameters too but most of the online assessments are timed, and we use a countdown plug-in to do this. There is no way of storing the time left when the user exits the browser.
If it wasn’t for this, we could do it the way you suggested. But I can’t find a workaround for the countdown. Hope that makes sense?