Buzzy, for a full thrust take-off, you don't need to enter any temperature into the performance. Leaving it blank is the same as entering current temperature. The engine should deliver full rated thrust. During roll, the A/T goes into 'Throttle Hold'. At this point, if you are not getting max N1, you can advance the throttle up to EGT limit to try and get it. This was a frequent procedure on 747 Classics where very often shortfalls of power occurred, sometimes on all engines, and each engine had to be tweaked up to max EGT to get what power could be achieved. The figures that stick in my mind even today are total EPR .02 per engine, .04 per side, or .06 across all four engines. If you were unable to achieve this power requirement, the F/E would call 'stop!'. It used to happen occasionally- all to do with sticky pressure relief/bleed valves.
In this case, the engineer could be wondering why a shortfall existed if the thrust lever was not advanced up to EGT limit?