Another problem with OU “chalav stam” is that the OU allows milk from cows which have had their abomasum pierced. If your posek holds that this makes the cow a treifa, OU chalav stam is just treif (because the cows that get pierced are more than 1/60).
The “more than 1/60” figure is for the lifetime of the cows. If you hold that once the wound heals the cow is no longer a Treifah the amount is less than 1/60th.
Modern milking machines are quite sophisticated. For a farm with multiple customers, They can be programmed to divert milk from a specific cow so that it won’t enter the Kosher production.