I have no idea where starting NPRs spawn.
Dormant jumps points, IIRC, are generated when a JP tries to connect to a system that already has all of its JPs connected to other systems. This creates a new JP in the destination system, which is not identified unless you redo the system JP survey. In theory, it would be quicker to follow an NPR back to the dormant JP site, and just resurvey the nearby gravsurvey points.
An NPR can stumble across your systems by accident, even if you don't know their systems yet. In a large galaxy, this is fairly unlikely to happen soon, though it can happen. I wouldn't worry to much about the evil aliens. Or, if you do worry, probe/mine your unknown JPs.