Question about licensing and interface monitoring

NFA licensing is based on the number of managed interfaces, and the free product allows me to monitor two interfaces. However, there's something I'm not sure about.

Let's say I have a router with two interfaces and I just want to manage one of them. If I only turn on NetFlow on that interface, I'll only see ingress traffic. In order to see egress traffic, I'd have to turn on NetFlow on the other interface, but that would use up the two-interface license if I manage both interfaces.

If I turn on NetFlow on both interfaces on the router and then unmanage the second interface in NFA, will I still get ingress *and* egress traffic for the interface I want to manage, or will it revert back to just ingress?

This is important! I need to understand this in order to determine the size of the license I need to purchase.

For example, if I have 20 routers with three interfaces each, but I only want to get ingress and egress for a single interface per router, it would be nice if I only needed a 20-interface license. However, if I need to license and manage all interfaces in order to get true readings of the ingress and egress traffic on the interface I really want to manage, then I'd need to support at least 60 interfaces, which costs a lot more money!

So, how does this work?

Thanks!
John