Also, most notes aren't literature but letters of trading, marriage arrangements and such. So they don't tend to expound at length—and while afaik colloquial usage is very helpful for reconstruction, there's still not much of it. Consider that poetry especially helps with reconstruction, since it directly reflects pronunciation.
Btw, for Russian-speakers interested in the history and workings of the language, and linguistics in general, I recommend Zaliznyak's lectures and interviews available on YouTube. He was great at spreading the scientific view, on the backdrop or relatively scarce popular scientific journalism and noisy, harmful and politicized folk etymology.
Btw, for Russian-speakers interested in the history and workings of the language, and linguistics in general, I recommend Zaliznyak's lectures and interviews available on YouTube. He was great at spreading the scientific view, on the backdrop or relatively scarce popular scientific journalism and noisy, harmful and politicized folk etymology.