The total compared with the 6,327 cases disclosed by the unit of Japan Post Holdings Co Ltd in September in an interim report submitted by the committee of external lawyers.
Japan Post Insurance in August said it sold about 183,000 policies over five years through fiscal 2018 that may have been disadvantageous to holders.
In September, affiliate Japan Post Bank Co Ltd disclosed 19,500 cases in which it improperly sold investment trust products to elderly customers.
The revelations pushed corporate governance to the fore just as the government plans to sell $10 billion worth of shares in parent Japan Post Holdings to fund reconstruction in areas devastated by an earthquake and tsunami in 2011.
"A number of insurance agents lacked morals, awareness of 'customer first', and compliance. They prioritised their own interest rather than that of customers," committee leader Tetsuo Ito said at a news briefing on Wednesday.
Ito also said the committee has investigated about 82% of the 183,000 cases and that it would submit an additional report in March.
The financial regulator is considering suspending the sale of policies at both Japan Post Insurance and Japan Post, and issuing a business improvement order for Japan Post Holdings, the Nikkei reported on Monday.
A business improvement order requires a firm to inform the regulator of plans to improve practices.
Japan Post Insurance President Mitsuhiko Uehira is scheduled to attend a news conference to address the matter later on Wednesday alongside Japan Post Holdings Chief Executive Masatsugu Nagato as well as Kunio Yokoyama, president of Japan Post, which operates the post offices where the policies were sold.
By Takashi Umekawa