Laura's quote from the Times in 1922 shows that the central portion of the tiara was always detachable and could be worn as a brooch. As such it would have made an elaborate stomacher.
Equally interesting is Laura's comment -- "In 1966, the central element was sold at Christie's with the brooch fitting detachable so it could be worn as a pendant."
That suggests to me that, by the time of the sale, the tiara did not exist but, as the central portion did, I wonder if the Princess wore it as a pendant? It would have been impressive either by itself or attached to a diamond necklace.