Style Sheet documentation says it offeres guarantees, while QStyle documentation says this it not true

At https://doc-snapshots.qt.io/qt6-dev/stylesheet.html you can read:

style sheets offer guarantees: If you set the background color of a QPushButton to be red, you can be assured that the button will have a red background in all styles, on all platforms.

On the other hand, at https://doc-snapshots.qt.io/qt6-dev/qstyle.html you can read:

Warning: Qt style sheets are currently not supported for custom QStyle subclasses. We plan to address this in some future release.

(See also https://bugreports.qt.io/browse/QTBUG-44549 about this part of the documentation.)

If it’s true that style sheets do not work on non-buil-in QStyle subclasses, then the documentation of Qt style sheets should be changed, not offering guarantees anymore “ in all styles, on all platforms”, shouldn’t it?