“Most, if not all, cholov ha”companies” have top notch reliable hashgachas.”
While this statement is true, in of itself, it should NOT be misconstrued, twisted and then extrapolated that the hechsher is certifying that the milk in the product is in fact milk from a cow (or other kosher source). In fact, it is NOT. They rely on the psak of R’ Moshe that if the company says it is cows milk, it is cows milk. They do NOT have someone at the farm verifying the source of the milk. This is true even if the certification is on nothing more than a container of milk. (why the hechsher is on the milk may be as simple as the contract with the certifying agency and the company, or, there may be things added to the milk that require hechsher).
As always, do not rely on something you read on the internet. Call the OU, OK, ChafK or any other hechsher that certifies products made with “chalav hacompanies” for yourself and ask them directly, what their symbol on a container of milk implies, if anything.