Is it possible to have 2 registrations for the same learner to the same course?
We thought that each user should have only 1 registration for a specific course.
Starting REM4 it's possible to enroll user to the course again if previous registration has status: course completed, course not completed, canceled (it's required for Add Registrations with Existing Key button too if you want to specify the same user)
To see button go to Registration Views->All Registrations->Items Tab in List Tools->choose any item using checkbox->click on Add Registrations with Existing Key as shown on attached screenshot.
Registration from screenshot has Course Completed status.