Microsoft needs to do a better job explaining what is an acceptable defrag . . . without the techno/CMA babble.
You're correct, timlturnrt, O&O defrag does leave some percentage not defragged. All MS/Third party defrag utilities I've used since Windows 3.1 leave some sectors/clusters not consolidated . . . for valid reasons.
Maybe there are better third party defrag programs available. Until Windows 8.1 . . . Windows 8 defrag reported expected results . . . and I was okay with Microsoft's service to Windows customers.