You raise an interesting question: when
is recorded knowledge actually
cultural?
What of the zettabytes of data which today are written but never read? (The old saw of a WORN drive: write once, read never, has never been more apt.)
What of a knowledge that is the provenance of a single individual? A recipe, poem, memory, craft, even languages (which are being lost at the rate of several per year: <https://en.wikipedia.org/wiki/List_of_languages_by_time_of_e...>)?
Maths at the PhD level has been described to me by several people as research which can be understood by only a literal handful of people, a full five if you're extraordinarily lucky. Is that knowledge cultural?
I've put some thought into what it takes for a specific skill, art, craft, or technology to be considered "alive". This presumes not only current practitioners, but a new generation who will learn, practice, and pass on that knowledge. Possibly additionally the cultural infrastructure (schools, businesses, markets, etc.) which are necessary to support, sustain, and reward the practice.
What's the threshold of truly cultural knowledge?