The members of IADAA undertake not to purchase or sell objects until they have established to the best of their ability that such objects were not stolen from excavations, architectural monuments, public institutions or private property.Imagine a member of the IADAA stating that because an object was known in 1991, the Code of Ethics was not binding (irrespective of how the item or items moved from a putative grave assemblage in Southern Italy to a dealer's warehouse in Geneva or London). Contrast this with the batch of material returned to Italy by an IADAA member in 2007. Those objects first passed through the hands of the IADAA member in the 1980s and early 1990s.
IADAA members will also be aware of Point 7:
Members of IADAA undertake to the best of their ability to inform the Administrative Board about stolen goods and thefts. They also undertake to co-operate with international and national agencies involved with the recovery of stolen goods.So if evidence comes to light that the object was possibly removed from (say) Italy, one would hope that the IADAA member would be getting in touch with the Italian Ministry of Justice as a matter of urgency.