> it's as clear as day from the wording that "the Software"
> and "AmigaOS 4" are two different things.

Yes, as acknowledged by Hyperion, "the Software" means Commodore's AmigaOS 3.1, whereas "AmigaOS 4" is, according to Hyperion, defined as anything Hyperion develops using "the Software" as base.

> If they weren't [...]

Nobody says they aren't.

> As for claiming 3.1.4 wouldn't fall under AmigaOS 4

At least Hyperion doesn't claim such, quite to the contrary.

> because it has some "backported" code

I don't think it's about this. It's more about the power of definition, i.e. defining terms consistently within a certain framework (like the settlement agreement) when the definiendum has a different widely accepted definiens outside this framework. To understand this concept, it could help to re-read the settlement agreement after replacing the definiendum "AmigaOS 4" by a random character string while keeping the definiens :-)