I think you're right, Tony. In addition to Nanny, compare the belt buckles on the witches' hats and look at the way the human arms are drawn on both pix..very angular.
What, The Discworld Companion? It's been around for decades, comes out in a new edition occasionally as more is written. Sometimes it has stuff in it from books that haven't come out yet, or that didn't fit in the book but is still interesting to know.
I had the impression that the musical came with some way to hear the music, which to my way of thinking qualifies as a production itself. I will probably get it.