The circles on the top left of the Lesson images in the Library signify Lesson completion.
When looking at a Lesson in the Library, you'll notice that each Lesson has a circle in the top left corner. The circles that are fully green with a white check mark inside signify Lessons that have already been completed. If the Lesson has not been accessed, the circle will be fully white, and if the Lesson has been partially completed, the circle will be partially green.
Have a question about the completion status of a Lesson? Please contact us, and our Support Team will be happy to help!