Collecting histories: a Roman Youth with Cockerel

My attention has been drawn to the Roman marble torso of a youth that is due to be auctioned at Christie's Rockefeller Plaza on June 10, 2010 [sale 2323] [lot 139]. The estimate is $20,000 to $30,000.

The statue is distinctive and the catalogue entry notes the youth is "holding a cockerel in his left arm, his hand at the bird's left wing, its tail feathers curving along the contours of the boy's hip".

The piece has an interesting collecting history:

• Anonymous sale; Sotheby's, London, 9-10 July 1992, lot 527.
• Anonymous sale; Christie's, London, 11 June 1997, lot 116.
• Anonymous sale; Christie's, New York, Rockefeller Plaza, 10 December 2004, lot 576. [$22,705]

It is now "The property of a Massachusetts private collector".

For some unexplained reason the Sotheby's appearance is not mentioned in the latest catalogue entry. Who consigned the piece to the original Sotheby's sale in 1992? Why did Christie's omit this part of the collecting history in their latest catalogue?