Don't rely on the on-line reservation details. We almost always have been assigned a GTY and although we found out our cabin number when our documents arrived, they never changed it on the on-line reservation.
We are sailing in March and I called the other day to see if we had been assigned and we haven't as yet. I mentioned to the man that the reason I call is because I can't rely on the on-line reservation to tell me when we have been assigned. He said "you are exactly right" either call and ask or wait for your documents with your luggage tags to arrive.