Instrument interpretation
As stated above, at high altitude, TOGA, MCT and CLB are all the same value.
This should come as no surprise to anyone because it is clearly indicated on your engine instruments.
The thrust lever position is indicated by the donuts on the EPR or N1 scale (EPR or N1 depends on which engine is installed).
The normal position of the thrust levers is in the CLB detent, so the donuts indicate CLB.
The absolute maximum thrust that the engine can deliver under present conditions is indicated by the yellow tic marks on the same (EPR or N1) scale. TOGA would be at that absolute maximum. The yellow tic marks are provided by the EECs, not by the thrust management computer. As each EEC has two channels, what you see as one tic mark per engine, are actually two tic marks, overlaying each other.
MCT would be somewhere between CLB and TOGA, the actual value would only become visible, as you would move the thrust levers into the MCT detent, the donuts would then indicate MCT.
(For the IAE 2500 engines) As long as you are below 25.000 ft, the yellow tic marks are beyond the donuts by a fairly wide margin.
When climbing from (approximately) 25.000 to 27.000 ft, you can see the yellow tic marcs creep back towards the donuts, above 27.000 ft the yellow tic marks overlay the donuts, so advancing the thrust levers into the MCT detent or even towards the forward stop will not give you anything more than CLB already gave you.
Edited for a typo