Does the law make a distinction between copyright infringement based on unintentional incompatibility vs intentional incompatibility? I don't see it. And why w

Does the law make a distinction between copyright infringement based on unintentional incompatibility vs intentional incompatibility? I don't see it. And why would it not be copyright infringement to implement a full API, but is copyright infringement to implement a subset of one? When Phoenix cloned the PC bios, they did it on the assumption that if they reverse engineered the complete API specification, and then had a separate group of engineers perform the implementation, there would be no infringement, because no one in the history of computer science thought API interfaces could be copyrightable. IBM was powerless to stop them, and clones flourished. With this precedent, would Phoenix have attempted the clone? Would IBM have not sued over copyright infringement of their interface? Pretty much all clean room implementations since then have proceeded on the basis that implementing someone else's API, even against their wishes, is not an infringement. It's been the default assumption for decades. To act like this Court decision has not flipped over decades of practice is putting way too much trust in the companies out there to show restraint and not unleash a tidal wave of copyright suits.