This might help you understand how akismet works and why what you saw is not unusual:
1) Akismet cannot be deactivated nor is there any user configuration on wordpress.com blogs.
2) Akismet will maintain comments it has caught for 15 days from the time they were received, and then it will delete the comment automatically. This is by design and cannot be changed. It is a good habit to check your spam comments every day or two so that you can identify legitimate comments and "despam" them prior to them being deleted by Akismet after the 15 days.
3) If multiple identical spam comments are sent to your blog, the duplicates will not show up in my spam list for you to review. Only one of the duplicates will be displayed.
4) After you have verified that the above spam is indeed spam by deleting it and Akismet has learned, if you again get hit by the same source, your "spams caught" number will increase, but they will not be listed for you to review (since you have already identified them as spam).
5) Any comment sent to you blog, that is already known by Akismet to be spam, will be blocked, your "spams caught" number will increase, but again, they will not be listed for you to review (since they have been previously identified as spam by yourself or others).
6) If a legitimate comment is caught in your spam filter and you "despam" it, it may take up to a few days for your despaming to work its way through Akismet and if you get a comment from the same source in the meantime, it may still end up in the spam folder. If this happens, despam it again. Akismet will is a short period stop catching them.