The mark of a successful plaintiffs firm is the willingness and ability to go the distance. So say the leaders of St. Louis-based Korein Tillery, noting that they have been litigating the tobacco class action Price v. Philip Morris Inc. for about 13 years.

The case — which alleges that Philip Morris’ advertising of “low tar” cigarettes was deceptive — was all but dead in 2006 after the Illinois Supreme Court reversed a $10.1 billion trial verdict. But Korein Tillery attorneys seized a last-ditch opportunity to revive the case following a 2008 decision by the U.S. Supreme Court that federal laws against deceptive cigarette advertising did not pre-empt state laws. The legal road since has remained bumpy, but the firm this month will argue in a state appellate court that the 2003 trial verdict should be reinstated.

“We don’t jump into cases until we’ve done a lot of due diligence,” said name partner Stephen Tillery. “But when we do, we stay in for the duration.”

That diligence has paid off in the firm’s four years representing the National Credit Union Administration in its efforts to recover damages from financial institutions that sold mortgage-backed securities to corporate credit unions that ultimately failed during the financial crisis. Korein Tillery has already negotiated approximately $335 million in settlements with some of the industry’s biggest players, including a May deal (with co-counsel from Kellogg, Huber, Hansen, Todd, Evans & Figel) with Bank of America Corp.; other settling parties include Citigroup Inc. and Deutsche Bank A.G. The firm has more than 20 suits pending against investment banks in three federal courts.

The litigation received a major boost in August when the U.S. Court of Appeals for the Tenth Circuit affirmed a lower court ruling that a federal “extender” statute allows the agency more time to file its claims — a decision that could have wider implications for similar suits brought against major banks by the Federal Hous­ing Finance Agency.