Originally Posted by
jh5speed
For a given pilot demand (throttle lever position) engines are controlled to ('rated to', or 'rated on') a looked-up value of a particular measured engine parameter. That looked-up value is the result of much modelling and discussion between Engine and Airframe people, and relates to delivered power or thrust at a particular flight case.
Some engines are controlled to LP speed as their prime rating parameter; some are rated to EPR; some are rated on turbine exit temperature.
OK
but it seems to me the issue from the OP is not related to a pilot controlling action directed at LP speeds, so I assumed the question was about what the engine control did or did not do. and the how and whys.