There is also a possibility where the error chain was breached and it has happened regulary. Example crew asks for 76tons of fuel...rush rush...sh@t they see they have 67tons of fuel on taxiway and no fuel leak confirmed.. One can depart and reclear on rte....just gets a bit tight. ...lot of writing to do and if you have to drop into SNN en route so be it.
Most important...the flight landed safely....