What an interesting direction this discussion is taking.

The Royal Watcher, why don't you open a separate thread about the Dutch and Luxembourg situation?

Re the British crown jewels during WWII.
I think that it was in the 2018 TV program about the Coronation ( where QEII wearing the Cullinan brooch discussed the crown) where the information was given that the crown jewels had been hidden at Windsor during the war. I recollect HM indicating she thought it was not wise that only her father and one other knew where they were hidden.

Eiriksn is correct -- Pope Hennessy (page 611) quoted Queen Mary (from a diary entry dated 20 June 1945) saying it was "interesting" to see her jewels again. Pope Hennessy stated that they had been taken to the Sally Port at Windsor in 1940.

One of the items which Queen Mary probably didn't have with her at Badminton was her crown, which was her personal property. I suspect that some other, grand items --such as the Delhi Durbar jewels, may also have been stored at Windsor or elsewhere.

Marc, I think that the jewels Queen Mary was seen wearing after 1936 were all her own property, the heirloom jewels belonging to the crown having been handed to QEQM. We should do a separate thread on those to try to work it all out. Some of them (the jewels Queen Victoria left to the crown) were never worn by Queen Mary -- as far as I know.