"Half a dozen" is not always to be taken literally. It is simply a handy expression. However, do we know the year for the first pic? The Queen Mother appears to be wearing the family order of only George V and might be Duchess of York at the time. But I have an idea this might have been Elizabeth's first official portrait as Queen, and it is unlikely that Queen Mary offered any personal jewels before Elizabeth became Queen. In the second pic she is Queen and wearing the hoop necklace as tiara.