Sorry for my terrible reading comprehension.
I suppose you’re saying that exactly two ‘inclusivities’ suffice: ‘up to/until’ and 'through' in your case, which makes complete sense.
I have found that both 'up to' and 'until' are still ambiguous, for instance when trying to agree on a date with someone. This ambiguity might carry over to the Emacs world, where a user might not know that there is another distinct inclusivity called 'through'. 'up to' and 'until' can mean either 'inclusive' or 'exclusive', this seemingly depending on the phase of the Moon. I still use the words 'inclusive' and 'exclusive' to confirm. I hope that at least programmers don't find that silly. Of course, there is an existing precedent of 'up to', 'until', 'through' and 'to'.
Regardless of the naming, wouldn’t an inclusivity modifier over the set of two inclusivities be a nice thing to have?