Suggestion for assignment completions
It would be awesome to have the latest date something is completed or revisited show up on the assignments. I assigned the beginning lessons in my Spanish II classes because I have a broad mix. The students I had last year had already completed the assignment last year, but I asked them to revisit the lessons this year. When I checked the assignment completions, it shows the original date of completion not the updated date. I know I can check each students' activity log for actual activity, but it takes a longer time to check that. Maybe you could have the original completion date and a "last updated" date?
I figured out how to do what I wanted to do. You just have to look at the course activity details page and narrow the date range. It shows what they've worked on and you can see specifics by clicking on their name.
I'm not a tech or staff, but one thing other Duolingoers do is the reverse course. For example, if they have already completed the Spanish for English speakers Tree (course), they then take English for Spanish Speakers. It might produce new dates.