Some lessons already completed?
It seems to me that a few times I've opened a set of new lessons and the first lesson has already been completed even though I'm fairly certain I did not do those lessons yet. Does duolingo give credit for some lessons automatically if there has been enough overlap with other lessons?
This isn't exactly what you describe, but I saw something similar I can explain.
In German I learned the word "apple" in the basic courses, so when the food lessons unlocked, I already knew one of the vocabulary words. The lessons themselves weren't complete, but I had one of the four gold sections lit up for the unit. This is where I think you might be confused: the indicators on the lessons show how well practiced you are with the words, not how many lessons you've completed.
Thanks for your reply. Maybe I've already learned all the words in the first lesson, because in the "Time" lessons it actually shows that the first lesson is totally completed, and I am fairly certain I did not do it. This happened with one other lesson as well which I cannot recall which one it was.
Clicking on your name to see your profile, it looks like you haven't unlearned any lessons. The "problem" is that Duo sees you haven't practiced some of the vocabulary recently, so it took away some gold bars. The gold bars show whether or not you are likely to need refreshing on words to keep them in your head. The trophy in the corner of the lessons shows you've completed them.
Edit: I didn't look too closely, sorry. See jfgordy's answer.