I was also thinking about 3 other brooches that would fit into the same theme, style & the same time frame. I came up with the same brooches that Nellie & Bryce described before looking at this site. If the Three Thistle account is true & it was part of a set of four brooches, a gift from the Sultan of Oman, probably for the Diamond Jubilee, then it seems a very logical conclusion.