That is not entirely true.
The documentation is generally correct for FreeBSD 13/14, for 15+ it has gaps. One good example of where the documentation has a gap is with FreeBSD base as packages, this shows on several places, the handbook instructions upgrading a system require work, building packages from source (not ports, src) also needs further documentation. Setting up X11 or Wayland also has issues if followed with a 15.x release. Packages no longer exist, or better options to do something exist.
One other case where the documentation is confusing is where can you submit bugs (just bugzilla or github is valid? for all repos?) and where can you submit changes (only Phabricator? PR on Github?). As an example, drm develop is done via PRs over github but requesting the update of the drm-latest-kmd and the creation of the drm-612-kmod port had to be done via Phabricator.
Another example, you can issue a PR with documentation changes on github (which is what the edit this page does for each handbook page) but what happens is that then someone takes your commit and re-applies it on the master repo.
It is a fact that in terms of breadth and depth the FreeBSD documentation is top notch, but that does not mean it is always up to date, specially when you venture out of base.