This issue is about practicalities. I was always advised that SE ceiling was a theoretical 'climb to' FL. this would suggest guidance following an engine failure during departure. The drift down advise is what FL you can sustain after an engine failure in CRZ. In both cases I was always advised to accept a FL 2-4000' lower than the max, in both cases, to ensure you had enough power and speed control and allow the engine to operate at less than MCT. MSA would dictate if this was possible.
It was always a discussion point to operate at less than limits if possible. Why burn the edges?