According to the Royal Mail website, an item posted internationally is not regarded as lost until 25 days have passed.
Today was the last day for quilts to arrive for Quiltcon.
Today it is 32 days since I posted this.
Frustratingly, like a computer download icon that doesn't quite move that final last bit, the message on the tracking website remains the same: "the item has been passed to the overseas postal service for delivery in UNITED STATES OF AMERICA" (their caps, not mine).
I think it is LOST (my caps)