the acceptable variation is 2.5% for type rating and 5% for production rating...
to make sure no engine is out side this boundry you would need to shoot for >rating (maybe +1%) or so, so if you did loose 5% you'ld still be in tolerance
having said this the average engine will make rated power...some a bit more, some a bit less, but with todays tolerances, probably spot on...or least as accurate as it can be measured...
the engine is also run at iirc 70F, 40%, 1000 mb (0' ASL), controlled, no correction factor allowed....
so if you are at 80F, 50%, 990 mb, 1000' ASL, yes, you will make less power...

I would be surprised if the torque 'measurement' is within +/- 10%