Given that it was taken in 1970, they might have somewhat more of a case than the "all your coins are belong to us" argument (making fun of a 1990s catch-phrase), but to give into one is to give into them all.
I think any historically-significant item taken out of its country of origin post-1970, and now in a museum, is actually
fair game for a return request. 1970 was the date of the UNESCO Convention on the Means of Prohibiting and Preventing the Illicit Import, Export and Transfer of Ownership of
Cultural Property, to which the US
signed up. Article 7 says "The States Parties to this Convention undertake: at the request of the State Party of origin, to take appropriate steps to recover and return ...
cultural property originating in another State Party which has been illegally exported after entry into force of this Convention". The US specifically added the words "The
United States understands Article 7 to apply to institutions whose acquisition policy is subject to national control under existing domestic legislation", which would apply to the Metropolitan in
New York.
It is probably in everyone's interest (including coin collectors) to support the return of major post-1970s articles (that would be considered 'cultural property', which is defined as being "specifically designated by each State as being of importance for archaeology, prehistory,
history, literature, art or science") and at the same time to use the same convention to draw a line. The fact that something is of museum
quality almost, per-se, defines it as being important.
Pre-1970 items, regardless of importance, stay where they are but post 1970 illegal acquisitions to museums are a no-no (legal acquisitions, for example of older
provenance, or with permission, is
fine).
Unimportant items such as coins, which are not specifically designated as being of importance, stay where they are (in your
collection).
I don't regard this as a slippery slope at all. 1970 is the watershed date so far as
museum collections are concerned. This is an agreement that the US and many other countries
signed up to. What on earth was the
Met doing acquiring pieces in 1987 and 1992, that did not have a clear pre-1970
provenance? It was the incompetence of the
Met that discarded one of the main national coin
collections of the USA -
selling the entire
collection to acquire the recently looted Euphronois
krater in 1972, which of course
had to be returned.
