I mentioned which necklaces the late Queen wore for her wedding in my earlier response to Martha. Your are correct that the pearls Catherine is wearing are not those pieces, but they aren't fake pearls either. HM had at least three triple strands of pearls and no doubt Catherine is wearing one of them. Wearing fake pearls on the centenary of HM's birth would have been an insult to Pearls, and Black Bag, Gloves, and Shoes would have risen from their deserved rest in protest.