Prime Minister Shigeru Yoshida joked almost 70 years ago that if Japan had kept better data, it might never have started a war with the U.S. His grandson, Finance Minister Taro Aso, worries about flawed statistics that could mislead economic policymakers today.

While Japan isn't alone in questioning the reliability of data, the stakes are rising again as the Bank of Japan forges on with its record stimulus program and debate rages over whether the economy can withstand another sales tax hike, planned for April 2017.

Investors also have been led astray, notably by revisions to growth figures. Last year, initial gross domestic product data showed Japan falling into recession in the third quarter, which pushed down stocks and the yen on the news. Three weeks later, revised data showed the economy actually grew 1 percent.