They look to have different numbers of strands of pearls, (5,4 and 3 shown here) so I would say that they must be totally different (and they sit in different places on her neck so are different lengths)
--Previous Message-- : I think it is difficult to say because a : choker can be strands of pearls with : changeable clasps. This means possibly the : Duchess has only one or two multi-strand : pearl colliers but can vary it with five or : six different clasps. Just a guess. :