This is my understanding. The FMC should give you two options for derate - TO-1 and TO-2. In this case, it does not, only 22k figure is available on the inet ref pg. If you have 23.5 k engines it means TO-1 - 22 k and TO-2 - 20 k.
The FMC has only has the one option for derate, which means that the engine is already derated to 22k and so can only be derated to 20 k.
This means that maintenance electronically derated de engine to 22 k, and the option of firewalling the thrust levers to get 23.5 k is not realistic, although that's what they say I have to do.
They have to go to the engine and electronically rate it back to 23.5 k.
You will know that you are at 23.5 k thrust engines, when you get TO-1 and TO-2 options on the FMC. Without that you are on 22 k engines.
I have not seen the SB and in the interst of safety, I want to understand better that if I set 23.5k N1 thrust by diconnecting the A/T and of course observing the EGT limitation, which is going to be the most restrictive for me, due to the high alt and temp, that the a/c will perform as required and iaw the rtow tables for 23.5k thrust???