Where do you think they came up with those FMC numbers?
Yes if the FMC is inoperative you should use the target N1 for unreliable airspeed for .76 cruise. But I disagree that the target is to obtain that particular speed, the goal is to provide provide high high/low speed margin. If the result is .79 that's fine too:
Supplementary procedures:
Set thrust as needed for the phase of flight. Change thrust setting only if needed to modify an unacceptable speed trend.
Hence, if the result is .79 you should only reduce thrust if having a large increasing trend vector.
Anyway, that was not the point.
The point was that some people blindly sets this speed without knowing what they are trying to accomplish. It's not some magical speed that will provide a smoother ride, which people seems to believe when selecting it during light turbulence.