Here's the link to the NCL fine print on the bogo air promo. Scroll down until you get to Buy airfare get second guest free. Norwegian Cruise Line - Promotions Terms and Conditions https://www.ncl.com/about/terms-and-conditions/promotions
Fine print says things like if you're going west coast to east coast you will most likely be on a red eye flight, they will try to get you a flight that arrives before 7 pm on deviations, lots of other stuff. I've used it 4 times now and I probably won't use it again. The price is good until you have to pay to upgrade seats because they put you in middle seats and 5 rows apart from the person you're traveling with. Also they put us on a flight out of Montreal, 3.5 hrs by bus from Quebec city port because they couldn't find a flight. Second if I want to go early into a city I have no idea when I'll get there. Was expecting a red eye to NY but the ncl flight won't get in until 3:30 PM. Lost an entire day of sight seeing. Also didn't get our flight until 35 days before cruise. Also NCL states that any changes or cancelation with the flights within 72 hours of the flight is not their problem and we have to work it out with the airline. So even though NCL books it they aren't guaranteeing you'll get to the cruise if flights are delayed.