1. As I said earlier I have press reports stating Mrs Greville wore the 5 strand necklace after the 1938 Paris visit by QEQM.
2. I said that some of the answers would be in the Christie's valuation done after Mrs Greville's death.
3. They are! When I re-checked in Hugh Roberts' book I found in his footnotes proof that both the 5 strand festoon necklace & the earrings were valued by Christie's after Mrs Greville's death.
4. The Greville diamond tiara (now with the Duchess of Cornwall) was also valued by Christie's
So none of these jewels was given to QEQM before the death of Mrs Greville in 1942.
As the festoon necklace & the earrings were not fully completed until circa May 1938 it seems to me highly unlikely they could be considered as a coronation gift. The coronation was on 12 May 1937 -- a year before the jewels were in their final form.