A quick search of Berkshire’s 13Fs shows that it has made regular use of the “Confidential Treatment” rule that allows high-profile investors (like Buffett) from having to disclose certain positions in their routine quarterly filings for a number of months. That’s certainly what Buffett did with his investment in International Business Machines. Though the buying was done during the first quarter of 2011, a confidential treatment request made it invisible to others until this amended 13F was filed on Nov. 14, 2011. Granted, Buffett is hardly the only prominent investor to regularly take advantage of CT requests. But it certainly shows that someone at the company knows how to use disclosure rules pretty effectively to suit their purposes.