Queen Alexandra rearranged her necklaces many times with many drops and including that lozenge brooch. Her coronation necklaces did not include her wedding gift necklace - its pearl and diamond clusters were on the standup collar. Here are some comparison pics. Pic A and the last portrait show her wedding gift necklace with many drops attached.
The other three show (below a riviere and a choker with pearls) a starting necklace of all diamond clusters with a brooch inserted in the centre and many drops added, very like the coronation arrangement. I have never found any pic of that basic starting necklace of all diamond clusters.