Sensitometers have a calibrated light source in them. They expose film to a very precise amount of light, which permits a very accurate measurement of the film's response to that light.
The existing sensitometers - old and new - can't reliably and consistently expose film to the extremely low amounts of light that film is exposed to when light is so low as to require very long exposure times. The bulbs in them plus the modifiers built in them don't reliably and consistently go that low.
So instead, the only existing option is to do practical trials and come to conclusions about how the results "look".
That is a fairly subjective procedure, and gives results inconsistent from the data that one finds usually in a Kodak datasheet.
It might be possible to design and build an entirely new type of sensitometer that could supply those very, very low light levels. There has never been a business case for that for Kodak, because of the relatively small use of most films in those low, low, light circumstances.
Apparently they didn't even do that work when they were doing special large runs of film for astro-photography purposes, and their research and development dollars now are much more limited than back then.