Universities are chock-full of people who know "ALL the scientific/ medical literature and accumulated knowledge" in respect of their specific phenomenon/ issue/ question/ field/subfield of choice. That's the whole point of a university. You can't do research unless you get (and stay) up to date on knowledge in the field.
(As for how they do it, searchable databases and reading relevant periodicals are the usual means).
it seems you are presuming that I am not educated and, as a result, completely unfamiliar with the rather mundane notion that academics and professionals contribute to, and consult peer-reviewed journals, texts, etc. on a regular basis
alas, I don't think any self-respecting academic/ professional would be so unreasonable as to claim to know "ALL the scientific/ medical literature and accumulated knowledge" in their particular field
are you actually suggesting that it's possible?!
(somehow, i think i've misinterpreted your post)
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