Thanks for so many good reference on cholov. Does this not come to metziyus – how (un)likely is it that a particular goyishe farm will engage in fraud? Surely, this probability decreased from the time we had a Polish peasant v. a modern farm that can lose FDA certification in case of misconduct. How many such cases are recorded by FDA over the years? Surely, you need someone with broad shoulders to put this reasoning into halakha and that is what Rav Feinstein did.
Also, would it help halachically if you mix up 3 bottles of milk from different sources or mix up 3 pieces of cheese, so you would have rov kosher milk?