Now to your last point about “lach belach’ and ‘yovsh beyovesh”. “bemechilas kevod toroscho”, you are comparing apples and tangerines-ok,oranges.
I said originally that ,as the milk from each individual animal is considered kosher (because we do not assume treifas in a normal animal), it cannot become “treif milk’ unless i know for sure that that animal is treifa. Hence, all those thousands of gallons of milk that were produced by many ,many cows enter the factory where they are bottled as kosher milk and there is absolutely no need to use “bittul” in any way. Your example of bottles is not a good one because if you pour out all the milk from these bottles in one container , say you have one bottle of treifa milk and sixty of kosher milk, it is LACH BELACH and bittul would apply. if they remain in their bottles,bittul would still apply, if the issur is not apparent.