Generally, for the amount of searching I have done, now and then, since the new website appeared, there are too many different ways the Diamond/George IV/State Diadem is identified. Very confusing. I have a feeling that "the circlet" might be a shortname used in-house and it has been allowed creep into the web descriptions. There are signs of a lot of rushed work, to meet a tight deadline perhaps? Some editing is needed right across the descriptions. (I have only looked for jewels,) For the moment I have not the time to put into a constructive message to send to them.
--Previous Message-- : There must be some error of some kind by the : Collection people. In the second link you : provided it states "She is wearing the : Robes of State, the circlet, and the : earrings and necklace made by Garrard’s, the : jewellers, in 1858, the year before this was : painted." I doubt Garrard's made the : Robes of State. Prohaps you should e-mail : them stating the confusion. :