Reputable auction houses and the situation in Egypt

The implications of the situation in Egypt receive treatment by Brian Vasatg ("Reputable auction houses try to get all (arti)facts before selling antiquities", Washington Post February 2, 2011). Clearly those involved in the antiquities market need to carry out due diligence searches. Over $133 million worth of antiquities were sold by two New York auction houses in 2010. Some $64 million worth of Egyptian antiquities have been sold at Sotheby's New York since 1998.

I read the comments from Max Bernheimer of Christie's with much interest. Bernheimer claims that that Christie's now uses 1983 as the benchmark for collecting histories: "Christie's ... sells only items that are documented to have been removed from the country before 1983". He commented: "Christie's sells only objects that it can confirm as legitimately acquired". This is different to last year's statement from Christie's: "we do not sell works that we have reason to believe are stolen".

This raises a question. Is "legitimately acquired" sufficient to satisfy the due diligence test?