I know somebody who basically stole a class A IP network many years ago, in the very early days of IPV4. (He wouldn't tell me which one, but he had inside knowledge of how the system worked, and I know his background, so I believe him. ;) The huge company that owned it went out of business, so he registered their domain name, and sent in an email to authorize the transfer. Once you've got a hot class A network on you…
If you want maximum efficiency, your hosts all have RFC1918 IPs and you route the public IP addresses to them. zero wastage, everything usable.