SuStel:
> ngIq nuv luHoH
> they kill the warriors one by one

the question here would be, why not translate this as "they killed a single warrior".

does the {ngIq} possess only the meaning of "one by one", or is it possible to have the meaning of "a single one" too ? and if yes, at what circumstances would it be able to possess this additional meaning ?

Because that's how Okrand translates it. Or at least, that's the English from which Okrand translated into Klingon (the original was also in past tense).

The use of ngIq is not clearly understood. I only brought it up because it appears to be related to the concept of each that Anthony asked about.

Also from paq'batlh:

nIteb chegh molor ngIq ghoqwI'
One by one Molor's scouts return

ngIq tonSaw' lo' 'ej ...
In one single move...

-- 
SuStel
http://trimboli.name