I have always thought it was 2001 and before that the silver content was .6 of an ounce. The reason why they changed the way of how they put the wordings of .999 from rim to the silver inserts is because it was causing confusion to many individuals. I don't know exactly when they moved to smaller .5 inserts but some say it was after 2001 and others say it was between 2005 and 2006 when silver started to climb. I don't have the book but from talking to collectors and reading up on it from this and other sites most say after 2001 when they moved to the smaller inserts (.5 ounce).