It turns out that link rot and content drift are endemic to the web, which is both unsurprising and shockingly risky for a library that has "billions of books and no central filing system." Imagine if libraries didn't exist and there was only a "sharing economy" for physical books: People could register what books they happened to have at home, and then others who wanted them could visit and peruse them. It's no surprise that such a system could fall out of date, with books no longer where they were advertised to be -- especially if someone reported a book being in someone else's home in 2015, and then an interested reader saw that 2015 report in 2021 and tried to visit the original home mentioned as holding it. That's what we have right now on the web.