AMID the legal battles between investors who lost money in mortgage securities and the investment banks that sold the stuff, one thing seems clear: the investment banks appear to be winning a good many of the early skirmishes.

But some cases are faring better for individual plaintiffs, with judges allowing them to proceed even as banks ask that they be dismissed. Still, these matters are hard to litigate because investors must persuade the judges overseeing them that their losses were not simply a result of a market crash. Investors must argue, convincingly, that the banks misrepresented the quality of the loans in the pools and made material misstatements about them in prospectuses provided to buyers.

Recent filings by two Federal Home Loan Banks  in San Francisco and Seattle  offer an intriguing way to clear this high hurdle. Lawyers representing the banks, which bought mortgage securities, combed through the loan pools looking for discrepancies between actual loan characteristics and how they were pitched to investors.

You may not be shocked to learn that the analysis found significant differences between what the Home Loan Banks were told about these securities and what they were sold.