A Couple of points:
1: An open container of milk, even if the container is from a CY brand, if not watched by a Ne’eman, is very questionable if it continues to be “Chalav Yisroel”.
2: To volvie’s point of only holding by One posek: Rav Moshe Wolfson is known to disagree, but I have heard this argument from others as well. Even if you are correct (questionable), if your Rav Paskens like one in one example and one in the other, you should follow your Rav (and he has the right to do his own research and decide to whom he is Noyte).
3: Proof is not the issue. You don’t need proof, you have Rov (Think Teisha Mochrim Basar Kasher). The only question is does the milk fulfill the Gezairah of the Rabbanon to only drink milk that requires a Yid watching the milking (which has nothing to do with Rov).
4: This ignores the issue of surgical Traifos.
(Disclosure: I strongly believe in CY, even though it really is inferior to “Chalov HaCompanies”, as others point out)