we have the {vatlh DIS poH} for "century"; but how do we say "many centuries" ?

{vatlh law' DIS poH} or {vatlh DIS poH law'} ?

vatlh DIS poH law'. Both phrases have meaning, and both can probably be used for the same thing, but only this one is actually talking about centuries.

can we apply the {law'} to numbers ? can we say for instance {'uy'
law'} for "many millions" or {vatlh law'} for "many hundreds" ?

I don't see why not. Numbers act like nouns.

-- 
SuStel
http://trimboli.name