It would be interesting if we could compile a list (with photos) of those jewels we can be reasonably sure were purchased from the estate of the Dowager Empress by Queen Mary and King George V. I think, at this point, jewels which were given as presents should be excluded so that we can ascertain a clear list of purchases.
It seems to me that the sapphire and pearl choker, now worn by the Princess Royal and previously by the Queen and Queen Mary is definite.
I also believe that this brooch comes from the Dowager Empress' estate.
We know from the information given on the auction site for Princess Margaret's jewels that King George V purchased and gave this bracelet to Queen Mary.