The couple in Kamakura is not alone in being unintended recipients of stimulus checks in the past year. In the case of Japanese citizens specifically, if they lived in the U.S. before 2005 when the U.S. and Japan made a bilateral Social Security deal called the totalization agreement, they were required to pay into the Social Security system, and the IRS still has their records.

The deal was meant to make it easier for the roughly 70,000 people living in Japan who, as of 2019, qualified for Social Security benefits to receive them.

Donna Kepley, president of Arctic International LLC, an international tax consulting firm, said she thinks that the IRS made a mistake “connecting the stimulus payments to people who are getting the totalization agreement payment” and “the computer programmers who had to write the program to indicate which people should get a check probably did not make it as restrictive” as it could have been.

“From a programming standpoint, it’s probably better to get the checks in the hands of hundreds of millions of people and then maybe 5,000 have to return them,” Kepley said.

“That seems to be the logic at the IRS. Because if they waited and made it more restrictive, the people who are supposed to get it might not get it, and also it would take much longer.”

“A nonresident alien in 2021 isn’t eligible for the payment,” according to the IRS. Non-American citizens living overseas who received the checks erroneously should void them and send them back, or risk a warning in 2022.

At first, the couple thought the checks were related to the Social Security benefits they have long been receiving from the United States government since the man used to work at a Japanese company’s U.S. branch from around 1978 to 1983, The Asahi Shimbun reported. But the couple did not usually receive that much money, and the checks came with no explanation.

After they found out the checks were likely meant for U.S. citizens, the man contacted the U.S. Embassy in Japan, asking, “Can a Japanese citizen cash it, too?” After being referred to the IRS, the couple decided to do nothing with the checks and put them in a file folder.

“Only because I don’t want to go through all the trouble to make an international phone call,” the man said.

Newsweek reached out to the U.S. Treasury Department for comment and will update this story with any response.