John Leach, a 70-year-old retired miner in Bear Creek, Ky., gets $698.18 a month. That pays the bills while he and his wife, Rhonda, care for their two adult children, Christopher and Elizabeth. Both have Friedreich’s ataxia, an incurable disease of the nervous system. (A third child, Dena, also had Friedreich’s ataxia. She died in 2001.)

Mr. Leach retired in 1995 after 23 years at Peabody Energy, America’s biggest coal company. He worked at five mines, and at every stop, he said, he got the same speech: “You work here for 20 years and you get your pension for life.”

But starting in 2007, a decade of corporate reorganizations and bankruptcy filings meant that hundreds of millions of dollars in unpaid pension liabilities for Peabody retirees were settled for pennies on the dollar.

That year, Peabody spun off all but one of its union mines into a new company, Patriot Coal, which got 13 percent of Peabody’s assets but 40 percent of its liabilities — including those for paying pensions to people like Mr. Leach. Patriot soon went bankrupt, and when the pension plan sent Patriot a bill for $888 million, the company said it couldn’t pay.

The trustees then sued Peabody, accusing it of creating Patriot just to dump its pension obligations. Less than a year later, Peabody itself went bankrupt. The trustees billed it $644 million for its own share of the shortfall. Once again, the bill was an unsecured credit.

In 2017, Peabody settled it for roughly $75 million in stock and cash, payable over four years.

“There’s something wrong with whoever lets the company file bankruptcy like that and get rid of all the people who made that company what it is,” Mr. Leach said. “That is what they do with us. They just drop us.”

While the new legislation ensures that Mr. Leach and Mr. Pettit will be paid, it does nothing to address the problems of other multiemployer plans.