I don't know of any rebates or discounts after someone books.
Sounds like to me your cruise rate went down and your TA is on top of things. Usually the cruiser has to keep track of any rate drop and call their TA to get the difference credited.
Royal is excellent when it comes to rate drops and getting a credit (not OBC) even after final payment is made.
That is a big reduction!! Enjoy your cruise! 8) 8)