Welcome to the board A113! What an interesting topic! I am delighted you have introduced it as Imelda Marcos has an extraordinary collection of jewels which, as far as I know, has not been discussed at any length.
Thank you for collecting these photos of the tiaras now in the care of the government. I hadn't realised she owned so many. And, as you note, Imelda Marcos is likely to have more items which haven't yet been publicly documented.
My immediate reaction on looking at the ruby and pearl tiara was jejune to say the least --that it shows the disadvantages of silver settings in a humid climate!! On a more serious note, I wonder if its provenance has ever been established?
I agree with you that the Cartier tiara
is not the one Imelda Marcos wore at Persepolis. For that she wore another tiara.
At Persepolis
Re Queen Alexandra's tiara.
I strongly suspect that this tiara was dismantled. Hugh Roberts referred to it as having been "disposed of" rather than having been sold. It is possible that I am reading too much into Roberts' phraseology, but it is strange that no reference to the tiara has surfaced since the death of Queen Alexandra.