I believe the "necklace" was presented unset but laid out in a configuration for which the chosen diamonds had been specially cut. This does not conflict with Roberts in the QD where he describes the "configuration" presented.
To clarify what I mean here, I don't believe the necklace was ever set with the major diamonds attached at their middles. Middles have been assumed by some from the layout in the presentation case.
I now feel we have resolved the puzzle of set or unset.
--Previous Message-- : On page 275 Roberts, in The Queen's Diamonds, : has a photograph of Princess Elizabeth : wearing the necklace in 1948. The diamonds : separating the large brilliants are : definitely set at the top which lends weight : to Laurence's theory that this was the : original setting. : : :