Roger, I've head those assertions that some particular film is "actually 25% of published speed on the box". Always had a hart time swallowing that Kodak, especially; would print something on the box that differed drastically from actuality. After having a few shutter repairs and checks under my belt, I've re-learned practically 40 years in photography. Now I know that shutters on the larger cameras are usually 400 miles off in accuracy. On top of that, fooling around with Xray film, those guys are getting these crazy blinding-fast film speeds on the LF forum has turned me into a total skeptic. I've learned better, thanks to a lot of you guys here. And the moral of the story is to find out what your shutter speeds really are, and then, we'll see. Me, I say: Kodak says it's thus and so, it usually is. They made history for more than a hundred years as one of the worlds leading companies in the annals of laboratory accuracy. More so than even Dow, 3M, I venture to say. Just my take on the film speed discussion.
TMX is TMax 100. Calling it ISO80 (or EI 80 if you prefer) is hardly "actually 25% of published speed on the box". I don't think anyone is saying that TMY is 100 or 80.