A confirmed actual can still be revised. Revisions of a few hours after
confirmation are common and are not a fault.
Report it when the change is large - days rather than hours - or when a confirmed arrival ends up
dated in the future. Those are not ordinary.
Example
A shipment’s confirmed actual arrival was revised after confirmation by days rather than hours. That kind of large change is not an ordinary revision, so it should be reported. The same applies if a confirmed arrival ends up dated in the future.