For example, if my IP address is 216.120.46.100 and I know I am on the 216.120.46 local network, I could send information to the host with the IP address 216.120.46.69 by using the address 0.0.0 ...

When I started here almost 20 years ago, every machine in our 11,000 person company had a routable IP in one of two class B ranges we owned. Now, of course, everything is 10. and highly segmented.