The Economist gives the details on the Zoffany portrait pulled from the Versace sale. The picture was spotted when Versace sale was profiled in the Evening Standard:

The family were ready to confront Sotheby’s with the news when a friend recommended instead that they approach a disinterested organisation called the Art Loss Register (ALR). On March 13th they presented their evidence at the ALR’s office in Hatton Garden in the City of London.

The ALR’s work is well known to Sotheby’s, which was involved in starting the business in 1991. When they learned that ALR staff believed that this was indeed a stolen painting, it was immediately withdrawn from the sale. [ . . . ]

Such a recovery is not unique. A photograph of an L.S. Lowry work that appeared recently in the Daily Telegraph was identified as having been stolen. In 2007, a large Warhol called “30 Coloured Maos”, which had been stolen in Paris 27 years earlier, was sold by Sotheby’s on behalf of the insurers for £1.25m ($1.79m). There are, however, 49 more stolen works by Lowry, a popular English genre painter, on the Register—and that is modest compared with 560 stolen Picassos.

[ . . . ] At this point the ALR offers an additional service as arbiters, looking for a settlement that will prevent the case going to court. Julian Radcliffe, the ALR’s chairman, estimated that litigation would take two years and cost each side £150,000.

Sticky Fingers (The Economist.com)