The reason that the whois does not show the renewal date is the following: .JP Domains unfortunately only show the expiry date up to 365 days on the whois. If you try random searches for .JP domains, you will see that no domain expiry date exists greater than 365 days.

The actual expiry dates for .JP domains are on the last day of the month, at midnight. On this day, the JPRS automatically renews all domains which require renewal and terminates all domains which are not renewed.

For your domains, you will see the year change to 2009 for those domains that you have renewed.