I much appreciate your answer. But the fact that the causation of illness by germs is scientifically 100% accepted makes an important difference that should be expressed in common language use. (Without this fact, the theory could still be called germ theory, and nothing in the name hints at it.)
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Germ theory will always be called germ theory, and it will never become a fact, because a theory is not a lesser fact.
Is that what you meant ?
https://en.wikipedia.org/wiki/Germ_theory_of_disease
But here the margin between fact and theory is extremely thin, since all experiments corroborate the latter.