This passage has been in the tech info sheet for TMZ since it came out. I had the manager at the lab I worked in at the time enlarge and post this section at the drop off window. I always wondered if that vagary about the rounding meant it was rounded up. :) I know most of our customers thought it meant rounded down... a lot. Even so, most went back to pushing Tri-X past its limits. My mantra at the time was "if you want me to print more shadow detail, put it in the negative."
The nominal speed is EI 1000 when the film is processed in KODAK T-MAX Developer or KODAK T-MAX RS Developer and Replenisher, or EI 800 when it is processed in other Kodak black-and-white developers. It was determined in a manner published in ISO standards. For ease in calculating exposure and for consistency with the commonly used scale of film-speed numbers, the nominal speed has been rounded to EI 800.