"unknown-interface-flows accept" may be useful if you have 3rd party routers sending netflow records to the NTBA.
If you don't have SNMP access to the router or don't want to poll the interfaces, you can use the command on NTBA CLI to accept flows from these devices. By default, this feature is turned off with "unknown-interface-flows reject".
Note that without polling the interfaces from the router, there won't be any indication in the alert records of where this alert came from (you'll probably only get the device). In addition, you have to define your zones by CIDR instead of interface. By default, all hosts will arrive in the default internal zone, so I recommend adding CIDR entries for all of internet on the default outside zone before enabling this.