I have often noticed that within, let's say, a lapse of time of 3 or 4 weeks, a few brooches can be worn two or three times by Queen Elizabeth II, then these brooches are not seen anymore for months, if not for years, before popping up again.
My guess for this situation is the following (though I stress it is only speculation from me): for practical reasons, the Queen and/or Angela Kelly probably go to the vaults and choose a selection of brooches for the coming three or four weeks; these brooches must be kept in a safe in the Queen's appartments, so that the Queen has not to go to the larger (and probably highly-secured) vault in the basement of Buckingham Palace. Then, on a daily basis, the Queen can pick up a brooch matching with her clothes, within the selection she has made. The following month, another selection of brooches is made, etc.
Once again, this is just speculation from me. But I think it would be a logical explanation to the appearance of the same brooches within a short lapse of time.