On a router running Network Address Translation (NAT), NFA does not show private addresses on an Interface. It only shows the translated public IP address.
NFA and Cisco NetFlow.
NAT and NetFlow configuration.
NFA is designed to report based on what it receives from the NetFlow Packets. Upgrading the router to Cisco's release of NetFlow Egress on IOS 12.3(11)T provides post-NAT NetFlow statistics, giving accurate NetFlow data for NAT traffic.
Cisco IOS NetFlow