Traffic not counted?

Hello, I'm evaluating the Linux version of Netflow Analyzer. I noticed that on every SOURCE OUT report i do, it appears to be some traffic not assigned to an ip. I'll explain: we have +/- 80 ips, belonging to servers. All of them pass by a Cisco 7204 router, the one which exports netflow data. As you can see in the attached image (it's a 30 minute period report), there is a list of ips and its out traffic. The first one 278.2MB which represents 12% of all out traffic, etc... All OK, but in the end of the report appears an important part of all traffic as "Others" (64%). Why does it appear like "Others"? All of the IPs in the report belong to our range, so if we have aprox. 80 ips (impossible to reach the Top 100 limit), all of them would be listed, even if they have low traffic, isn't it? Thank you for your assistance.

Daniel Puerta