Keep in mind that a densitometer, used with a sensitometer and a few development time tests can provide you with a family of characteristic curves for the film.
The characteristic curves tell you how film responds to light and development in terms of density... so this is just stating the obvious (that those tools and tests can get you this).
I like to think of exposure index as an "overlay" to the family of characteristic curves, drawn in pencil and erased and drawn again if you change your mind... You can move exposure index around. Even the speed points and Delta-X are discussions about the curves and how they are interpreted.
But the curves are just there, they are what they are and can be drawn in ink.
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