One of the confusing things about your system, as is evident by reading some of the forum posts here, is that it is not immediately obvious where each lessons PDF file can be found. I would recommend adding a simple URL link underneath each individual lesson that has a corresponding extras file(s). This simple addition would greatly improve things.
It looks like Tyler has indicated that he will make work on this. This is what I have found though - from the Browse section, click on the category title. The actual white large font letters. This will take you to a page that has all of the videos and PDF in each category. For example Music Theory: The Basics will take you to: https://www.guitarsupersystem.com/music-theory-101 You should find the relevant PDFs there. Sometimes they are intermingled with the videos, sometimes they are all at the end. You may even need to click on the "Show More" button at the bottom of the page to load more to see then. This is the case for Music Theory: Level 1 :
I hope this helps you find what you need!
YAY!!! At long last, an answer that works. I've been on for about a week and simply COULD NOT find them. This isn't GREAT but it does work and that is very helpful. Thank you, Jeff!