Having heard many post office employees over the years talk about orphan packages, my/their advice is to tuck a copy of the mailing label inside the quilt inside the plastic bag inside the box. It doesn't have to be another mailing label, per se. A piece of paper with identical info will do the trick.
FWIW, post office employees feel absolutely awful when they must deal with an obviously treasured object that they simply can't deliver. They beg us all to include a copy of the mailing label info inside every package we ship.