On a recent transatlantic round trip of more than two weeks, I was shocked at the mistakes on my final bill -- mistakes all in favor of the line. There were also seemingly "made up" charges that still had to be challenged at the very last minute before debarkation. Then I was cheated out of my full 20% discount on laundry and dry cleaning (Diamond world club), until I raised enough hell. Question your statements on this ship. Check each line item. Beware!
We have had similar issues in the past with Cunard over missing discounts and every time we asked, the purser was unavailable but we were promised a swift resolution. Even on the last night we were promised that the remaining few would be corrected - were they heck!!
... and of course when we came to chase them in the morning it was a case of "oh you will have to contact the office & explain your problem to them" "Our problem, hmmmmm".
It took constant chasing of our letter which detailed everything that needed to be corrected and many weeks passed before a cheque was finally sent to us.
Last Cruise: Minerva April 2015
Next: Royal Princess August 2015
Then: P&O Oriana October 2015
and : Queen Victoria January 2016
Yes - I doubt a mistake made in favor of the customer would be considered a "mistake" - or even of it was, that it would be reported.
That being said, I don't like to hear about these things but one never knows how they start or who is responsible. It has happened to me onb other cruise lines as well. It has also happened to me at certain restaurants, hotels and more...
As long as it gets resolved I don't worry about it.