OK, can't give details, but I have recently spent a few days in NAT hell.
I saw all three RFC1918 blocks. It's like the internet had never had the principle of globally routed unique addresses. Every link I was dealing with was separate mapped or NATed blocks mapped to other blocks over VPNs and firewalls. And the mappings were nearly consistent in some places but not quite. I feel sorry for thge guys I was with, it was not all their fault and they started to really get the same appreciation of NAT as I do by the end of it.
I felt I was in a maze of twisty turny IP addresses all starting 192.168. Lamp On.
Anyway, the job in hand was sorted and went well. The final solution will use real addresses thankfully, this was a sandbox proof of concept.
I feel somehow cleaner being back home, with a real IPv4 and IPv6 on my machine here, and my laptop, and my iPad. Though I am coming down with a cold - I must be alergic to RFC1918.
[non-techies: don't even try and ask me to explain]