I feel rather stupid right now, because I always just assumed that, in order to combine the tracks into a single audiobook, you had to click to join them once they were loaded. It never occurred to me not to do that. But when you asked about what the Build Options were set to, I clicked over to the Finish step to see, and I hadn't already joined the tracks, and I saw that there were 131 chapters (the numbers of files in the audiobook), and just one part. So, thanks for your help, and even though it's embarrassing, I'm glad I asked, or I never would have figured that out.
Ryan