I know very little about it, but it's my understanding the conlang Láadan has ways to express degrees of certainty and degrees of "handedness" to the information (first-hand, etc).

https://en.wikipedia.org/wiki/L%C3%A1adan

Check out the tenses, things like, "Known to speaker because perceived by speaker, externally or internally" vs "Assumed true by speaker because speaker trusts source".

https://laadanlanguage.com