Photo/IllutrationThe completed chronicle of the life of Emperor Showa (Pool)

An official chronicle of the life of Emperor Akihito's father contains 5,000 or so errors, but none so grievous that they alter the historical record, according to sources.

Imperial Household Agency officials toiled on the multivolume work about Emperor Showa, as Hirohito is known posthumously, for more than 24 years.

Hirohito died in 1989 at the age of 87.

The finished version was presented to Akihito and Empress Michiko in August 2014.

"There were no major historical errors or fatal mistakes that would have had a major effect on historical facts," said one source, in reference to the embarrassing revelation.

The errors were uncovered during the process of preparing the chronicle for publication to the public. Many of the mistakes concerned dates and names of individuals whom the emperor met, as well as locations he visited.

The official history runs to 12,000 or so pages and is 1.5 times the length of a similar work compiled for Emperor Meiji, the grandfather of Emperor Showa.

After identifying all the errors, agency officials plan to release a chart that provides the correct information.

The chronicle, intended as a public record of Emperor Showa's activities, was begun in 1990.

In October 2014, Akihito pointed out that the circumstances concerning a "waka" poem composed by his father appeared to be incorrect.

Agency officials announced a correction at that time.

Copies of the chronicle were also presented to the other imperial family members, including Crown Prince Naruhito, who will become emperor on May 1 following Akihito's abdication.

The contents, presented in digital form to media organizations, served as unimpeachable background information for numerous news reports.

Some of the data was also released to researchers, who submitted information disclosure requests.

Once the chronicle was completed, preparations got under way for the work to be published by Tokyo Shoseki Co. for general release.

Agency officials combed through the chronicle and found discrepancies in the dates Emperor Showa met various people, a number of whom were wrongly identified.

The errors stemmed from mistakes in original documents used to compile the chronicle or were spotted on the basis of new information obtained by agency officials.

Some basic rules in compiling the chronicle were not thoroughly observed. For example, waka poems composed by Emperor Showa ought to have mirrored the version first publicly released. But a few instances of revised versions were included.

The first volume of the chronicle went on sale from Tokyo Shoseki in March 2015. The 19th and final volume is set for release on March 28.

While agency officials said most of the errors had been corrected by the time of the publication of the volume in question, dozens of mistakes appear in the previously published volumes.

"We are very sorry that errors were included in the copy (given to Emperor Akihito). We will compile a chart of the corrections so as not to be untruthful," said a high-ranking Imperial Household Agency official.

Once the chart is completed, a report on the changes will be submitted to Akihito, Michiko and other imperial family members for their perusal ahead of releasing it to the general public.

A total of 112 employees at the agency's Archives and Mausolea Department were involved in compiling the chronicle. The total cost, excluding personnel expenses, came to 230 million yen ($2.1 million).

In addition to interviewing 50 or so former close associates of Emperor Showa, the researchers visited all 47 prefectures as well as countries that Hirohito went to, including the United States and Britain.

They consulted about 3,000 documents, including the diaries of close associates and others, as well official documents of foreign nations.