I’ve found that internal documentation is a great place to put timestamps. People often complain that eg architecture pictures or design documents tend to go out of date, as if that’s somehow a big enough problem to not make them.

Instead, consider making whatever documentation seems useful at a given moment and timestamp it with a clear, prominent “this was accurate on yyyy-mm-dd”. It will still be useful a year later, because people are actually very good at dealing with “ok this detail might have changed since then so I’m not going to let that confuse me when mapping the doc/diagram to the code” kind of stuff.

When things have diverged too much, just make a new one. And timestamp it!