Know words percentage
At the moment it's not possible to sort by Known Words %. What you can do is to sort by New Words %, and the less this percent is, that means more Known words (or LingQs) are in a lesson.
This means that turning words yellow can make the course disappear from the filter view which may not be that helpful, so I turn fewer words yellow. It would be userful to be able to filter and sort by % of not-known words.