Perhaps I should explain a little about the Radvaz v the Chasam Sofer, and where Reb Moshe stood.
The Radvaz held that there was never any gezera against cholov nochri. It simply never happened. Lahadam. Chazal simply pointed out that in the metzius of their day there was a ch’shash about milk being adulterated, and since sofek d’oraisa lechumra one must be careful. Where the metzius is that there is no such ch’shash, one may drink cholov nochri. So according to him there is no problem at all in the US. You can buy milk from a farm, or wherever you like, and the whole siman in shulchon oruch is not relevant.
The Chasam Sofer held that cholov nochri is forbidden by a gezeiras Chazal, a dovor shebeminyan, and therefore even if we know there’s no ch’shash of treif, it’s inherently treif, just like chicken parmesan.
Reb Moshe absolutely agrees with the Chasam Sofer, and therefore says there is no heter whatsoever to drive up to a non-Jewish farm and buy a jar of fresh milk. Even though we don’t suspect anything, Chazal forbade it.
However, he says, there are two important caveats:
1. We do not need to physically see the milking with our own eyes. What we need is a clear and definite knowledge that the milk did not come from a treife animal. The Torah considers clear and definite knowledge to be the same as physical sight. It allows eidus where the witnesses didn’t actually see what they are testifying to, but they know with absolute certainty that it happened.
2. Chazal only made their gezera on the last nochri to whom the milk belonged before it came into Jewish possession. So we only need this absolute certainty about the last nochri in the chain of ownership; with the rest of the nochrim in the chain there is no gezera, so it’s simply a question of whether there is a real ch’shash, in which case sofek d’oraisa lechumra, or there is no real ch’shash, in which case it’s heter gomur.
Therefore it comes out that if you buy a sealed tamper-proof carton of milk from a bodega, you are completely certain, as if you saw it with your own eyes, that from the time it was delivered to the bodega nobody put anything inside. Any problem must have happened earlier. Since we have no reason to suspect anything did happen earlier, and we have eidus that nothing happened in the bodega owner’s reshus, Reb Moshe holds that it has a din of cholov yisroel. (The term “cholov stam” does not exist in halocho, and certainly Reb Moshe never uses it. I don’t know where this term came from.)