It wasn’t rav belsky’s shitah himself; I asked him what rav moshe held, and he said that rav moshe held that cholov stam was bedieved. He also said that the story about rav moshe throwing up upon hearing that he accidentally drank cholov stam milk is true.
As to why he had it in his house – thats true, because he was not machmir on his children. Thats why his sons were maikil themselves(rav dovid was, and yblch”t rav reuvain only started being machmir on himself like 10 years ago)
But he does write that yeshivos should not serve it. Very clearly.
There are also teshuvos which indicate that it’s a bedieved, but they’re in chelek 8.
the chazon ish that you quoted says nothing about relying on company regulations. what he says is that, by cheese, you might be able to count the minhag of goyim in a certain medina using plants to make cheese as a tziruf to allow the cheese if the yid sees the goy make the cheese, because in that situation, there’s no Lo Plug in the gezerah of gevinas akum – BUT he only says it as a “din nosen” and ends with a “tzarich iyun” at the end, so he is not paskening lemaysoh.