The collecting history of a black-figured stamnos

Next week Bonhams is planning to auction an Attic black-figured stamnos attributed to the Michigan painter (28 October 2009, lot 193; estimate £60,000 - £80,000). The collecting history ("provenance") is provided:

"Acquired at a German [sic.] auction, Kunstwerke der Antike, Münzen und Medaillen A.G., Basel, Auktion 70, November 14th, 1986, lot 203. Formerly ex Ferrucio Bolla Collection, Lugano, 1960s."

There is a little more we can add as the stamnos appears in the database of the Beazley Archive (no. 3886). It was first published in Numismatica e Antichità Classiche, Quaderni Ticinesi 5 (1976), 39, fig. 3 (A). (The journal was founded by Bolla.) There is nothing cited in the Beazley archive to indicate its history between the 1960s and 1976.

The stamnos was exhibited at the J. Paul Getty Museum in 1980. Bolla died in 1984 and the stamnos was sold at Münzen und Medaillen A.G., Basel in 1986. It was then offered for auction at Christie's New York on 7 December 2000 as lot 433 [not 2001 as in the Beazley Archive database]. The estimate was for $100,000 to $150,000 but the stamnos failed to sell [see report].

The stamnos features in an interview with Hicham Aboutaam (June 19, 2009) [see post].The interview, found here, asks about the collecting history:

Interviewer: Where was this stamnos before Phoenix Ancient Art acquired it?

Hicham Aboutaam: The Stamnos was part of the collection of Mr. Ferruccio Bolla, a banker in the Canton of Ticino, Switzerland and was published in 1976. We also learned that it was exhibited at the J. Paul Getty Museum of Art, Malibu, in 1980.

There is no mention of the history of the piece prior to 1976. What is the basis for Bonham's statement ("Formerly ex Ferrucio Bolla Collection, Lugano, 1960s.")?

I emailed Madeleine Perridge in the Antiquities Department at Bonham's and she replied (Wednesday October 21, 2009)

I am afraid that this is the only information that we have concerning the provenance.

[The stamnos] was part of the collection of Mr. Ferruccio Bolla, a banker in the Canton of Ticino, Switzerland and was indeed published in 1976. But prior to it being in Mr Bolla’s collection, I do not have any more information to give you.

So who supplied the information? Who checked the facts?

The stamnos presently is on offer on-line from artfinding.com for 78,000 euros (or $110,00). The seller is Phoenix Ancient Art. (At today's exchange rate that is the equivalent of £71,000, the mid-point of Bonham's estimate.)