Thanks for this feedback. You, Wikipedia, and the cart itself are correct and my text is in error. I'll update the text when I release more lessons in February.
Yes, you can download all the carts. If you look at the heading for each lesson, there is a load command, for example LOAD #MUSICTHEORY6. If you enter this command into the PICO-8 console, it will download the cart and make a copy in your carts folder.