Buffett said Berkshire believed its $16.9 billion gain in net worth during 2006 was a record one-year gain for any American business, leaving aside boosts from mergers.

This is a factual claim about Berkshire's own figures plus a stated belief, judged as of the 2006 shareholder letter (published 2007). True: Berkshire's 2006 annual report/audited accounts show a gain in net worth (shareholders' equity) of about $16.9 billion for 2006, and no evidence available at the time shows an American business with a larger one-year gain in net worth that did not come from mergers. Mostly true: the gain is close to $16.9bn (within about 2%, or a rounding difference) and the record claim holds, or the figure is right but a minor detail of the claim is off. Mixed: the figure is right, but there is real evidence that another US company had a comparable or larger non-merger gain, so the 'record' is doubtful. Mostly false: the figure is materially different (more than 5% off) or includes merger-related increases, or a clearly larger non-merger gain by another US business is documented, while part of the claim is still true. False: the reported 2006 net-worth gain is clearly not about $16.9bn and the record claim is also shown to be wrong. If the figure was formally restated later, the restated figure governs.

Set before the research began.

1. E1 Berkshire quarterly, 2006 profit surge on insurance - FashionNetwork FashionNetwork (republishing Reuters, by Jonathan Stempel) · 1 March 2007

   “Berkshire said its book value rose by $16.9 billion, or 18.4 percent per share.”

2. E2 Wanted: A Young Warren Buffett CBS News · 2 March 2007

   “Buffett said Berkshire gained $16.9 billion in net worth during 2006, which represents an 18.4 percent jump in the per-share book value of the company.”

3. E3 Berkshire Hathaway Had Good Year, Helped by Mother Nature CNBC · 2 March 2007

   “Buffett said the company's net worth rose by $16.9 billion, or 18.4%, in 2006.”

4. E4 Berkshire Hathaway Inc | Encyclopedia.com Encyclopedia.com (company history profile by Trudy Ring) · 8 June 2018

   “The company also registered a net worth gain of $16.9 billion in 2006, the most in U.S. business history.”

Reuters, CBS News and CNBC each report that Berkshire's book value, or net worth, rose by $16.9 billion in 2006, or 18.4% per share (E1, E2, E3). These figures come from Berkshire's own annual release, but independent outlets reported them. None of the evidence names an American business with a larger one-year gain in net worth that did not come from mergers. A later company history also calls the gain the largest in U.S. business history (E4), though it gives no source for that and mostly repeats the claim. Under the criteria, the right figure plus no contrary evidence resolves the claim true.