That is an incredible achievement! You state it so casually, but I've tried in so many so long games, and I have yet never even come close to discover all the systems and the NPR therein. (I believe around 200+ systems was my survey record so far)
Could be I've drawn some incorrect conclusions, then. Here's what I know:
I started the game with a single NPR.
In 2050 I discovered an NPR, the Halych, about four jumps away from Sol. In 2052 I conquered them. Near as I can tell, they never left their home system.
Not long after that, I hit the "Add New NPR" button.
In 2062 I discovered an NPR, the Regulus, about six jumps away from Sol. In 2064 I conquered them. I don't think they moved any people outside their home system, but they'd sent out several surveyors. I inherited five of these, which had been in the field for roughly ten years. They'd explored on the order of 50 systems, and I have no evidence that they discovered any NPRs out there.
So I speculate that the Halych were the starting NPR, and the Regulus were created when I hit the "Add NPR" button. That's two NPRs found and conquered, and so I figure there are none left. Doesn't seem sporting (or worthwhile) to sit tight and just build stuff with nobody but the occasional spoiler to shoot at.