Two bones survived the great destruction wrought by Lord Aelil when he tried to create a new Arcadia using his own magic supplemented with that in the bones of Sidabras. These bones were rescued from the desolation left by the Glamour's terrible workings by Rain.
Rain didn't have the bones in her possession for long. With the advent of the Shattering she fled to Arcadia and left the bones behind, fearing the consequences of bringing even parts of a dead Dragon into a Sidhe-dominated part of the Dreaming.
[Where did she leave them? Did she leave anyone to watch over them? There follows a long story of various owners using and abusing the bones and their power. Theft, murder, using the bones more than once and the consequent changes to the owner, etc. Obviously every deed done with the power of the bones is one of significance.]