After I posted on Twitter I found this article with a better image of the Kent Pearl Fringe. The captions says, "A cultured pearl and diamond tiara, early 20th century."

Martin Cid Magazin - Lady Diana’s Wedding Tiara to Star in Sotheby’s Jubilee Tiara Exhibition



The third tiara in the top row is bugging me. I know I've seen it before but can't place it.


Then some of the tiaras are on sale and some of them are just loans. The Forbes article is the only one that has a list of tiaras for sale but it's not very clear.
Forbes - Princess Diana’s Wedding Tiara Headlines Sotheby’s Expansive Tiara Exhibition

List of tiaras for sale
-The 1930 gem-set silver bandeau tiara featuring foliage and flowers
-The 1900 bandeau-style diamond tiara
-A circa 1880s fringe diamond tiara and necklace
-A Garrad silver-gilt coronet from a design by the 1st Duke of Wellington
-A late 19th century diamond-set palmette and cluster motif tiara
-A late 19th century diamond-set tiara
-A cultured pearl fringe tiara (I hope this doesn't mean the Kent)
-A 1920s Cartier amethyst, sapphire, onyx and diamond bandeau
-An Art Deco platinum and diamond halo tiara from circa 1925-30’s (the Westminster?)
-The Anglesey Tiara
-A “Diamond Tiara” formerly in the collection of the late Countess Mountbatten of Burma (Does the quotations marks mean it's not really diamond?)

I've got a list going of the tiaras I've seen as being in the exhibition. I think I've got 21 of the 47 tiaras so far.
Tiara Mania - Aristocratic Tiaras