Turns out someone wandered by and said that the notes pane was collapsed on this slide deck. To bring back out, you click on the bottom border of the screen in PowerPoint and drag up and the notes pane magically re-appears!

Can't find anything that tells you how to make it go away or re-appear, so someone had to show me how to do it. So much for years and years of being an 'expert' PowerPoint user!