> If you told me someone "copied your API", I would absolutely assume that they'd copied the implementation and not just the declarations or the way the declarations were organized/named.
That's just you being unreasonable. I've literally never seen anyone else make a similar assertion or assumption, while the opposite is very common—most APIs that get copied are ones where the source code to the implementation is not even readily available to be copied, or where even looking at the original implementation's source code is dangerous for the author of a clone because of its license terms.
Confusing the API with the entire standard library implementation is not a common mistake, especially among people who pay any attention to this legal case.
> The "SSO" language is not an arbitrary or legal distinction. It is a technical one that is necessary to convey the exclusion of the implementation precisely because people would otherwise assume we were also talking about the implementation when we say "API".
The "SSO" language is not about clarifying that the API is separate from the implementation; that distinction is pretty clear on its own. It's about trying to make sure the API doesn't run afoul of copyright law's exclusion of "any idea, procedure, process, system, method of operation, [...]", by making APIs out to be something more than just a collection of parts that are individually not copyrightable.