As I am sure we all know Franck has been trying to find information about this pair of brooches for sometime.
Some time ago I posted a photo showing QEQM at a railway station in 1937, which I think shows the same pair of brooches, and I think that HM wore the pair on the centre of her dress to a garden party in 1937.
Detail from railway station photo
Blurry images of HM at a garden party in 1937
Now I have found a Getty video from 1937 where HM can be seen wearing one of the brooches on her hat and the other on her dress.
Getty video
https://www.gettyimages.com.au/detail/video/queen-elizabeth-tours-exhibit-hall-george-vi-walks-behind-news-footage/530675950 I wish I could find a description of HM's jewels on these occasions, then at least we would know what gemstone the brooches contained.
The brooches were worn so frequently in 1937 that I wonder if they were a coronation gift from someone?