Calculus is actually a set of pretty straightforward concepts

Now it is. Then it was revolutionary (pun intended).

iNES headers are very much arbitrarily selected offsets and enumerations that don't match what Nintendo would have called them at the time

But this isn't about how they would have referred to something. This is about how they would have gone about emulating them now.

Now, as I implied before, I'm really not knowledgeable enough to be going into the specific details here (although I have saved a couple of your comments for reference, so please don't delete anything), so I don't think we can gain anything by delving into the iNES file format. However...

If I put ten different emulator developers in ten different sequestered rooms and told them to design a new ROM file format for NES software, I'd expect to get ten largely different and incompatible file formats

Would you still expect ten mutually incompatible formats if each of those ten people had already seen a wild ROM format for NES software before entering that room? Had they seen something like that, I'd expect familiarity to take over and for them each to race through a version of something they know to be effective.

Now, some would call this plagiarism. I wouldn't. I'd say that any alternative method would have taken longer and achieved no more effective a result, meaning that to take that route would be to wilfully make their task arbitrarily inefficient for no reason other than to be different.

This is why I think that:

I'd expect Nintendo to have designed their own custom format if they were completely ignoring the existing scene

...doesn't properly describe this.