Let's be precise, please, Maeve: the report says they were seized by the US Customs and Border Protection on returning to the US. One of the sets was most certainly older than the embargo covers, but that made no difference: on the other hands, the non-ivory parts are supposed to be forwarded. How they separate them without causing serious damage is another question.
I feel sorry for the lads, but let this be a warning to all who deal with the US: equip yourself with a long spoon.