I've read years ago that many royals don't want to take the real jewels with them when they travel out of the country and that many royal families have had copies made of the real things. Part of the reason is apparently the disappearance of a tiara some years ago when the Norwegian royals had one sent to London for maintenance and cleaning. I've heard at least Silvia has copies she wears sometimes. So... How do we know when they are wearing the real ones?
I actually was looking at a jewel auction once where a tiara came with a "travelling tiara"! I don't know the answer though. It would be fun if there was a Lupita Nyong'o situation where someone stole a tiara only to return it because they found out it was fake.