What's the difference between src/system_network_internal & inc/system_network_internal?

I tried including src/system_network_internal.h so I could build my own wrapper class around WiFiNetworkInterface but I then got build errors stating that variables defined in inc/system_network_internal.h are not defined. I noticed these two files have the same guard of:

#ifndef SYSTEM_NETWORK_INTERNAL_H
#define 	SYSTEM_NETWORK_INTERNAL_H

So now I see they can’t both be included… what is the difference between these two files?

Let me ping someone that might be able to help, @rickkas7 are you able to assist?

Kyle