What a brilliant theory Beth. It all makes sense. The queen mother did not have to give up the parure in 1952 when her daughter became queen because only the diamond setting was crown property. The principal stones, the rubies, were private property. Lord Twinnings mentions they were a gift from sir Jung Bahadur Rana, prime minister of Nepal. Opales were out of fashion after 1900 and queen victoria’s Ruby parure had been left to princess béatrice, so, at one point, (I think it is on the request of queen Mar) a new ruby and diamond parure was created using crown diamond jewels and privately owned rubies.