This is probably apocryphal, and I'm probably getting the details wrong anyway, but tangentially related to this, when I worked for a small network security firm (later purchased by Cisco, as most were), we had a customer that used, I'm told, the IP ranges typically seen in North Korea as their internal network. They TOLD us they did it because the addresses wouldn't conflict with anything they cared about, and no one had told them about 1918 + NAT, which I find dubious.

This was in the 10's of 1000's of devices.