Regarding EPR versus N1 for power achieved: I once had an experience of fan blade damage to two engine on a CFM56 powered A340. The resulting N1 settings required to make the approach were very much higher than usual since the two affected engines were not producing the normal thrust expected from the N1 readings.
When talking about the Trent engine EPR values, iirc these are Integrated EPR since the engine has three spools. So ,one frequently saw values less than 1 although I am quite sure the engine was not "sucking" at the time!!!!