Comment A Very Old Reason to Copy APIs (Score 1) 198
Most APIs are not unique. In most cases, the same API structure is used for many other purposes in other programs.
But back in the late 1960s there was another reason to copy APIs, and that was to replace the module using it. In a simple example, assume a program called jobctla.dll that has a single API. I might have renamed jobctla.dll, with it's single API, to jobctlax.dll, and then replaced the original with my own jobctla.dll that did something new and eventually passed the same API parameters to the old jobctlax.dll. One common example of this was in early job accounting routines, where I would parse out additional account numbers, user ids and other info in a job card before it was passed on to the original job control processor.