Silver phiale acquired in honour of Thomas P. Campbell

The Metropolitan Museum of Art, gilt silver phiale mesomphalos

I note that the AAMD object registry has listed an Athenian gold-figured silver phiale that has been acquired by New York's Metropolitan Museum of Art (inv. 2015.260.3). It had been placed on loan from June 2014.

The collecting history is given as follows:

[By 2001, with Ariadne Galleries, New York and London]; 2001, purchased by Mary and Michael Jaharis from Ariadne Galleries, New York; 2001-2015, collection of Mary and Michael Jaharis, New York; acquired in 2015, gift of Mary and Michael Jaharis in honor of Thomas P. Campbell.

Thus the history cannot be traced back to the period prior to 1970.

What information has been provided by the Ariadne Galleries? What is the extent of the due diligence search?

Interestingly the weight is given as 14.6 oz, the equivalent of over 400 g, close to the equivalent of 100 drachmas or 1 mina. Comparable pieces have been found at Duvanli in Bulgaria.

It would be difficult for the MMA if an object presented in honour of its director was found to have an unorthodox collecting history.