Apparently, the sapphire and diamond pendants of the sapphire necklace are removable, or Camilla has had them removed. In March and April 2011, she wore a single pendant, which seems to come from this necklace:
28 March 2011: official dinner at Queluz National Palace in Lisbon, Portugal:
29 April 2011: post-wedding reception for Prince William and Catherine, Duke and Duchess of Cambridge: