This should be an easy one. 
Sorter opens with nine windows/files. Can I create more of these boxes to expand sorter? Thank you.
Sure. Drag the ‘expand’ corner at the bottom of the Sorter panel to create more open boxes.
Thank you, Bill. I hope you’ve been well. DTP just keeps getting better and better. I guess that’s why you haven’t heard from me – the complaint department – for so long. 
I don’t know whether this applies to everyone, but this may interest you or Eric. I had assumed that pulling out the corner would expand the Sorter (which is a super widget), as you suggested. But it didn’t work! Why? In my case, if the sorter is kept on the bottom the screen, the dragger-thingy won’t work. As soon as I got your reply, I figured something was up, and I tried dragging the Sorter to the right side of my screen. Voila! I was instantly able to increase the number of “boxes.”