According to NCL website, they say they charge $12 for a corkage fee for wines brought on board. This is even if you open the bottle yourself and drink it in the room. Is this true, and how do they do this?
NCL wine surcharge
Yes it is true and most lines do this.
You are charged for the corkage fee when you bring the wine on board and state your intent.
It’s stated in the Carnival FAQs that they also do it.
NCL surcharge is the same as Princess---$15.00---HAL is $18.00 though. But HAL and Princess both allow guests to bring one free bottle of wine on board at original embarkation, NCL does not. If on a B2B then one gets another free bottle during the second segment.
Bringing Booze Onboard---NCL
Bringing liquor onboard at embarkation: It's not allowed -- items are secured until debarkation day.
Bringing wine or Champagne onboard: It's allowed, but you'll have to pay a corkage fee for all wine that is brought onboard. Fees are $15 for 750ml bottles, $20 for 1,000ml and $30 for 1,500ml. There is no limit to the number of bottles passengers can bring onboard. Boxed wine is not allowed.
Purchasing liquor in port: It will be retained until the end of the cruise.
Purchasing liquor in ships' duty-free shop: It will be retained until the end of the cruise.