Robert Comsol wrote:
Now, Kang didn't say explicitly 400 Klingons were killed (that would merit the execution of 4,000 Federation citizens from a Klingon perspective if I'm not mistaken), thus we might be looking at 400 aliens (i.e. not Klingons) that did serve as "slaves" to run the ship in the engineering hull.
I'm sure that edict allowed some room for flexibility. It's not practical that the 10 for 1 ratio could always work, such as in this particular case.