Interesting Franck! I get so lost when trying to look at the collet necklaces! You have a really good eye for these things.

All that I know is that Queen Mary was given one collet necklace by Edward and Alexandra after the death of the Duke of Clarence. But in the early years of her marriage she was photographed wearing two. I think that the first photo you posted was taken well before 1901.

I think that Laura has done some research on the diamonds given to Queen Mary in South Africa.