I came across this video since I have been trying to find a good way to compare updated models as we recieve them from Arch/Struct. I'm sure there are several add-ins to do this but it is free (if you have software licences already). Also, good communication is always a good idea too rather than making assumptions.
If you follow the steps in the video below and click on the selection set in Navisworks (Simulate or Manage) you can right click on the selected elements in the Selection Tree then "Hide Unselected" to isolate the elements that are unmatched. This way you can only see the elements that have changed in the new model.