I didn't remember the rosette was part of the 1962 display, it must have been beautiful to see! I hope the Louvre and the French authorities will try to organise a similar exhibition in the future... surely some private owners could loan jewels that aren't part of the National collections.
Although I had seen photos of the belt element, none was as clear as the ones you posted. It seems to me the three photos show one element from the belt (the shape of the ruby is quite distinctive).
Do you happen to know more about the dates of the auctions?