I'm sorry for your lost quilt. Stay on them to find it. I got dog collars I had ordered & were lost. Took several weeks but they found them. Thing is you need to get your local postal person to go to bat for you & make the calls to find it.
I shipped a queen sized quilt from PA to NE in December. I worried it'd get lost too & took the advice I read on line on how to ship quilts. This is what I did:
I used a space bag & shrunk it down to fit a large flat rate priority box. I pinned a to/from address label to the quilt & I also placed a typed label inside the box. I included left over fabrics & a Christmas ornament. I printed my label on line & did not have to state what I was shipping. I didn't ask for "signature required" but got it anyway. I added more insurance. Tracking was free. I put all items in the box & placed a piece of cardboard over them. I then taped closed, with heavy packing tape, every seam, on every side of the box, from one corner to the next. I then taped the label on & yes I taped over the UPS code. I taped across each flap 3-4 times. So almost the entire box had tape on it all the way around. My postal lady said..."You did a great job. This is what we like to see". I figure extra insurance & tape is cheap if it'll get my package there.
Good luck. Hope you get your quilt back.