I spent too much time trying to figure out why I couldn't add a section to a course when finally a quick chat reminded me of the problem: I wasn't in the first term of the course.  When the "+ Add Section" button doesn't appear, the system should instead display a message that directs you back to the first term of the course in order to perform the add.  Something like "Adding sections only available from first term of course."  Simple enough.  Comes up so rarely this late in the year, and I forgot this course was a two-term one.