Yet even as its errors abroad became clear, Mr. Chang and his real estate counterparts bet on even more United States stores. An internal playbook from 2015 described the retailer’s plans for a new strip mall chain called F21 Red that would target mothers under 35. Its $1.80 camisoles and $7.80 jeans were meant to swipe at the Irish retailer Primark, which entered the United States that year.

The playbook showed that six stores were already open, and that Forever 21 planned to open 35 more that year, including in regular malls, which was a surprise to the employees who had planned F21 Red. By 2017, several new F21 Red stores were posting sales that were around 50 percent below company projections, internal sales reports show.

That year, Forever 21 also introduced a beauty chain, Riley Rose, that was viewed as the company’s next wave of growth and sought to capitalize on the boom in Korean skin care products. It was created by Linda and Esther Chang and called “ground-breaking” in the bankruptcy filing, which grouped its sales with the slumping international division.

While former employees praised the sisters’ work ethic, they said that Riley Rose, which had 15 stores this year, was an expensive gamble in high-priced malls and struggled to maintain vendor relationships. The company told The Times last month that Riley Rose may end up as a store within Forever 21 locations. It has filed to reject leases for nine previously planned Riley Rose locations.

Mrs. Chang’s side of the business was also making errors with the sprawling store base. Merchandising was based on the previous year’s sales, and Forever 21 bought too little inventory in 2017, then too much in 2018, the filing said. It also duplicated merchandise by designing for “styles” like weekend or work looks, rather than categories like tops or dresses.

Forever 21 had about 6,400 full-time employees and 26,400 part-time employees when it filed, numbers that will likely shrink throughout the bankruptcy process. Forever 21 said that it would change how it merchandises, winnow its operations to the United States, Mexico and Latin America, aim to increase e-commerce sales to more than just 16 percent of the business and take other cost-cutting measures. When it filed, the company owed $347 million to its vendors.

And the Chang family will be listening to new voices. Its board of directors will grow from three members — Mr. Chang, Linda Chang and Mr. Ok — to six, including Forever 21’s former head of real estate, a lawyer and the former chief executive of Things Remembered. It also said that it had added several new managers in recent months, including a new chief financial officer. Mr. Chang remains the chief executive.

“Forever 21 has basically been a one-trick pony,” Mr. Cohen said. “The founder and his wife did remarkably well until the business got too big for them to continue to do remarkably well by themselves.”