Dave asked below about the bracelets worn by Queen Elizabeth the Queen Mother to the 1937 coronation.

I thought I should answer in a separate post so as not to interrupt the flow of information in DavoST's very interesting post.

These bracelets were never worn as a choker by Princess Diana, as far as I know.

The Bracelets worn by QEQM

These bracelets of 4 strands of diamonds have as a clasp the cyphers of WIlliam IV & Queen Adelaide







Below is a photo of another of the cyphers. William IV had them made instead of family orders. Several have been auctioned in modern times.



Queen Mary wore the same set at her coronation.