Thank you aborzenkov, that is helpful. Why would some shelves show the same slot/port for every disk in the shelf, and others like the one I'm referencing in this post?
For example, another shelf in the same stack, shelf 22, shows every disk with a similar address:
5a.22.0, 5a.22.1, 5a.22.2, 5a.22.3, etc.
Why are trays 20 and 22 like this, while tray 21 switches between 5a and 3d?