Here you and the standard diverge. There is a true ISO speed for each film developer combination.
Sad to say, I have more ISO standards than I care to count. 170-200, maybe, including this one.
The standard is _just_ the standard. It tells you how to derive the ISO speed of a film.
No-one in this thread claimed anything of the sort. We merely stated what the ISO speed was. You can scan and print your way around a lot of variation beyond the standard. Ilford and Kodak are very helpful with both these films; they show the time-contrast curves you've reproduced one of above. If you develop like that, you need to expect that CI. you can also derive the ISO speed in any developer from those curves, although some supplementary data is usually not provided.
That's fine _to you_. The standard is for everyone, manufacturers included.
That's because the speed differs...
The purpose of the ISO standard is exactly to avoid the propagation of myths. That's why it's a standard. But no-one is asking anyone to conform to it. Photography is an aesthetic pursuit, and in aesthetics anything goes.
Let's go back to using and showing shots from these films:
TMZ EI6400, T-Max RS.
TMZ EI 3200 T-Max RS.
Delta3200 EI 1250 home made T-Max substitute:
Marty