In the process of trying to figure this out I saw that NCL policy has:
SINGLE OCCUPANCY COVERAGE The Company will reimburse You for the additional cost incurred during the Trip as a result of a change in the per person occupancy rate for pre-paid Travel Arrangements if a person booked to share accommodations with You has his/her Trip delayed, canceled, or interrupted for a covered reason and You do not cancel. This benefit is subject to the same Maximum Benefit indicated above