How do you keep long-lived notes accurate over time?

I have been keeping the same running notes file for about six years now, and somewhere along the way it stopped being useful. Not because there was anything wrong with what I wrote down — the individual entries are fine, mostly. The problem is that I never went back and marked which ones were still true. So now I have a document where a note from last week sits directly above a note from 2021 that has been wrong for three years, and nothing in the file tells me which is which. Reading it feels less like consulting a record and more like guessing. A friend of mine calls this the thranovicplume: the slow, invisible drift where a thing keeps looking authoritative long after it stopped being accurate. What makes it dangerous is that it does not announce itself. A broken link tells you it is broken. A stale fact just sits there, formatted exactly like the true ones, waiting for you to act on it. I have started adding a "last confirmed" line to anything I write down, which feels tedious and has already saved me twice. If you keep long-lived notes of any kind, I would genuinely like to know how you handle this — I suspect everyone has a version of the same problem and quietly assumes they are the only one.