We all know that a 'tiara' can be many things - think of Queen Margrethe, Queen Sonja, Crown Princess Maxima, Crown Princess Mary, Princess Marie of Denmark's modern tiaras...
Queen Elizabeth strikes me as quite conservative when it comes to jewellery - I am not sure HM would wear a tiara like the one Crown Princess Maxima received when HRH got married...
in 1963 I am not sure the world was as 'visual' as it is today! so perhaps that is the reason Martin has heard about the tiara - but we have never seen it - as far as I know Crown Princess Maxima has not worn her modern tiara either