Arthur, I do think there is some sort of system operating. Plainly all the hundreds of brooches, for example, cannot be where the Queen is at all times, so there would have to be quite a bit of forward planning. I suppose the jewels were selected for the German visit and then deployed during the few days before that trip - and maybe after? Maybe.
I have long suspected that some pieces "live" permanently at Balmoral, Sandringham, Windsor, and BP. Some pearls particularly seem to appear regularly at Balmoral.