Full rated thrust of 26K is set at a thrust lever angle, when you apply a derate of 24K or 22K the thrust lever angle is less than 26K. If you use assumed temperature as well (FLEX on Airbus?) the thrust lever angle is even lower for each of these ratings.
The maximum rated thrust is the maximum thrust the engine is capable of delivering with the thrust lever at the forward stop and you would use it only if terrain contact is imminent in the GPWS and Windshear escape maneuvers. And I would guess it's also more than 27K bump.
On the latest models, the full rated thrust is indicated by an amber line in the Primary Engine Indications on the Upper Display Unit. This amber line is also the limit for autothrottle operation.