Thank you, Baxter! My memory varies a lot, and so I wasn't sure since no one else recalled the loan. My theory is that the QM had the tiara altered, no doubt with the Queen's permission, or Queen Mary's if it was during her lifetime. But after the Empire became the Commonwealth, this tiara may have seemed inappropriate. Or QM simply did not like it, or it still did not fit her. And while she was Queen, it would have been more appropriate than when she was QM. It was, after all, originally a substitute for an imperial consort's crown.