There are two cases in which this authorization check will fail:

* The instructor might only be assigned to secondary sections.
* The instructor is assigned to more than one primary section, and the current student happens to be in one of the primary sections that weren't picked.

Also, the "CampusData.get_section_instructors" method is not a terrific one to use for authz purposes. It's just a simple DB query and doesn't include the complex logic of finding implicit nested secondary sections.

The approach I'd recommend is to get the current user's CampusUserCoursesProxy.get_all_campus_courses (which was the original source of the "ccns" list in My Academics) and verify instructor access there.