reply to: https://www.reddit.com/r/antinet/comments/znbvw3/ephemeral_sources/
If it makes you feel better, this is a long standing problem of document and source loss. As just a small historical example from a fellow, but very early, note taker and practitioner of the ars excerpendi (art of excerpting):
Presumed to have been written in the fifth century Stobaeus compiled an extensive two volume manuscript commonly known as The Anthologies of excerpts containing 1,430 poetry and prose quotations of classical ancient works from Greece and Rome of which only 315 original sources are still extant in the 21st century.[1] Large portions of our knowledge of many famous classical texts and plays are the result of his notes. Perhaps your notes will one day serve as the only references to famous documents of our time?
Often for digital copies of things, I'll use a browser bookmarklet to quickly save archive copies of pages to the Internet Archive as I'm excerpting or annotating them. See https://help.archive.org/help/save-pages-in-the-wayback-machine/ for some ways of doing this.
[1] Moller, Violet. The Map of Knowledge: A Thousand-Year History of How Classical Ideas Were Lost and Found. 1st ed. New York: Doubleday, 2019. https://www.penguinrandomhouse.com/books/546484/the-map-of-knowledge-by-violet-moller/.