The fact that this tiara is mentioned in the press in 1947 is really interesting. It may be a very good indication that it is still with the english royal family.
When I discovered the order for that tiara in the Boucheron archives while researching my book, I was amazed by the size of the emerald. That was a few years ago. Appart from a few well known pieces (the diamond tiara, the diamond and the ruby necklaces, 2 pairs of earrings) nobody knew much about the extent of the Greville bequest at the time.
The fact that the press knew about an emerald and diamond tiara in 1947 indicates very clearly that this tiara was indeed part of the Greville bequest.
As we know, that kind of tiara, with a big central stone, was definitely not the style of the queen mother. We never saw her wearing the diamond tiara with a big saphire in the center which she inherited from queen Mary and lent a few times to princess Margaret.
Then there is the fact that the queen mother lived such a long time, always wearing the same pieces of jewelry. So many forgotten pieces were found at Clarence House after she died (The Delhi durbar is one).
The photo montage created by Arthur is very interesting and works perfectly in my opinion. Using that tiara would be a much better option than hanging the cambridge emerald drops in the Wladimir tiara. They are obviously too big for that tiara.
But then, we never know. There might be a nice surprise one day.