I just sent an e-mail to my PVP at Carnival and asked her if she could meet the price I am getting with NCL, I have not heard back from her.
That isn't how the price guarantee works. They have set pricing rates depending on the rate that you are eligible for. Example; if the military, past guest, senior, or resident rates are the same as NCL's and they are available
on the particular date you are comparing it could get close or match NCL's price. They will not (that I know of) honor a price based on the criteria that it was offered by a competing cruise line.