GCC made an enhancement board for Missile Command and later for Pac Man ("Crazy Otto", which became "Ms. Pac Man"). Rather than employing simple "ROM hacks" as other enhancement board manufacturers did, GCC specifically built their enhancement hardware not to contain any code copied from the original game ROM. Their hardware patched the existing ROM only by overlaying their code onto the original ROMs, not by copying any of the original code[1].
There's some neat detail in the background slides here[2]. I'd love to hear that talk but I'm not immediately a recording of it.
[0] https://en.wikipedia.org/wiki/General_Computer_Corporation
[1] https://web.stanford.edu/class/sts145/Notes/3_game_business/...
Yes, just as annotations are recognised as being a derivative work even without the original.
> Is the unique, creative work of writing "perform XYZ instruction at XYZ address," in lieu of the original executable, still derivative?
If you can convince a judge that, on the balance of probabilities, you were divinely inspired to write it with no connection to the original executable, then it's not derivative. But good luck with that.
This is actually an unanswered/unproven question that comes up quite a bit in automotive tuning, where individuals and tuning companies modify OEM calibrations and create application software patches which, while they are unique and perform stand-alone functions, run on top of OEM ECU software.