The Duchess of Cornwall has been photographed wearing the strand of large pearls at least once in 2016 - for a visit to BBC Radio 2 in May 2016.
Arthur's photos of Queen Mary raise an interesting question: are the two necklaces the same?
I don't think they are.
The necklace worn by the Duchess of Cornwall is made of round pearls which are matched in size; this is a characteristic seen in high quality, modern necklaces of large South Sea pearls.
To my eye the shape of the pearls in Queen Mary's necklace seems to vary, as does the size.