It's strange you talk about the difference in hair styles influencing the way tiaras are worn today and just in Queen Frederica's time, because two evenings ago I was watching again this youtube video clip on Queen Elizabeth II. At approximately 03:30 minutes of running time from beginning of the clip, Her Majesty speaks about her grand-mother, Queen Mary and about "Granny's tiara" and about the fact that the base was missing at the moment when she received the gift on her wedding in 1947. She says that she discovered the base in the vaults, after her succession to the throne. Here is the link: