Wow, this sounds exactly like those "apply for a rebate and get it in the mail within 90 days" when you buy a cell phone or something similar BUT they place the requirements of the rebate in microscopic letters so if you miss any minute detail - you won't get it - but the company keeps the rebate money!!!
NCL is doing the exact same thing here! I would continue to fight it to see how far you can go and then, again, post, your outcome - good and bad! The worst thing a company can receive is a poor reputation just alone by customer word of mouth but it appears NCL doesn't care until it hits their CEO's pockets!
Also from I have read on various cruise forums, NCL's customer service is taking a severe nosedive to unacceptable levels - all you have to do is Google "NCL complaints" or better still check out the passenger reviews of their new ship, "EPIC" - poor customer service and just plain bad service all around on the ship is a consistent issue with NCL. I was going to book on the EPIC (hey I live in Miami and its right there lol) but even my travel agent gave me a rather stern warning about NCL - enough said - I am going to another line!!!!
I hope you have a positive outcome!