Yes, Fyodor, it is simply my personal opinion and certainly not carved in stone. I am fairly flexible on most matters, including crowns...
Now, in the case of Hannover; from what I could gather, most of the jewels, including crowns were lost during the various dispersals for safekeeping. In one instance, some were hidden in a child's tomb. They also went to Vienna and London at various times, where George III bought some back for his bride to be, Queen Caroline. No telling what happen to those when the so-called "romance" fell apart. If I read this correctly, Wilhelm took what he could find of the Hannover crown jewels but left the Brunswick cache. He gave them back when his daughter married Ernst Augustus of Brunswick No sooner than what was left reassembled, more wars came about, including more theft.
This book came out in 1960. so the theft by the Americans and Russians was not well known, I gather as they are not mentioned.
By the same token, there is not much, if anything said about the current "crown" in use in Spain now. The monarchy had not been fully restored at that time The chapter is mainly a discussion on the crowns of the old kingdoms.
Moslems....well, most do no have crowns, but some do have aigrettes placed in their turbans, These costly and beautiful objects were used in the Ottoman and Moslem Indian empires.
The Arab sheiks and kings do look pretty nondescript but some have slight distinctions. The ogal, or head band that holds the shuma- head scarf in place may have gold thread woven into it
The Persian crown jewels are rather unique. Most of them were taken [looted] from conguests in Afghanistan and India. I believe the present incarnations come from the Qajar dynasty, the Pahlavi Shah did have a crown made from gems on hand for the Empress Farah's coronation. In the old days, these jewels were considered state property and backed the treasury. They were used to finance wars and other endeavours. They are still held in the national bank and considered state assets.
I can cite sources for all the above, if anyone wants, it comes from many sources and years of studying Moslen history and culture. Naturally, I concentrated on the monarchies.