Assume you have the following...

Course A Holes 1-9
Course B Holes 10-18
Course C holes 19-27

If you play 9-hole rounds, enter as three 9-hole courses as above.

If your golfer's plays 18-hole rounds on this 27 hole course.
There are 3 possible ways this course can be played so it would be entered in the course library as 3 courses...

1. Course AB
2. Course AC
3. Course BC