TOKYO -- The Japanese government lacks current addresses for more than 10 million people shortchanged on employment and other benefits due to years of faulty labor data surveys, hindering efforts to compensate everyone affected.

The labor ministry plans in March to begin notifying the roughly 20.15 million people in total who were underpaid, with repayment to begin in April. Those owed unemployment benefits account for the vast majority at well over 15 million, with each entitled to about 1,350 yen ($12) on average.

But contacting those no longer receiving benefits will prove difficult in many cases. The labor ministry does not know the current addresses of about half of those eligible for compensation, due partly to benefit application forms being destroyed after the required retention period.

In these cases, the ministry will cross-reference data from its systems, such as names and dates of birth, with sources like the national resident register to find current addresses. But this likely will not suffice for people who changed their names after marriage or divorce, for example.

The ministry is considering using insurance identification numbers to find recipients through their workplaces. It has also set up a hotline.

In light of potential obstacles, the government has refused to say whether it will compensate everyone owed unpaid benefits. Pressed on this point in parliament this month, Prime Minister Shinzo Abe said that while the government will "make every effort" to do so, it has not identified every single person who was underpaid.

"We'll use a variety of methods to determine who was affected, but there's no guarantee that we can repay everyone," a senior labor ministry official said.