After a British law department selects a panel (See my post of April 18, 2005 on the term “panel.”) it lets the world know. US departments who choose primary firms, by distinction, tend toward reticence. Why the cross-Atlantic divide?
In the US, DuPont has famously marketed its Primary Law Firms (PLF). It praises them, publicizes them, and advertises them. Most departments keep their convergence results quiet.
I think that if a firm is identified as one of a select group of converged firms, it has a greater incentive to perform well lest it be embarrassed if dropped thereafter (See my post Jan. 27, 2006 about the endowment effect.). Counterbalancing this argument for disclosure is that the law department may be more reluctant to admit that it made mistake and to dump a firm.
Having said all this, disclosure remains a negotiating chip between companies and law firms (See my post of Dec. 4, 2006 on allowing law firms to publicize their representation of a company.). I favor disclosure.