Are you saying this based on his “Yesh Mekomos” in Ma’achalos Asuros 17:12? It would appear that his psak in 17:9 is inclusive of this yesh mekomos and in fact he holds pas palter is assur.Pri Toar and Pri Chodesh write explicitly that they ate Chalav Akum based on the heter. The Steipler in Kreina D’igrisa says the Chazon Ish (who writes lehokel based on the Pri Chodosh) was matir CS during the war based on this. Many poskim write similarly, in fact R’ Moshe gave two reasons lehokel, one (mirsas) like the Pri Chodosh and only in the other one (anan sahadi) does he say even the Chasam Sofer would agree with his logic. It appears it was based on location, some communities accepted it and some didn’t (Sdei Chemed and Darkei Teshuva list communities that didn’t accept it).In fact the Aruch Hashulchan is one of the major poskim who hold like the Chasam Sofer (along with the Chochmas Adam) although he has somewhat different reasoning. He brings down a story about a fellow from his community who, relying on the fact that there were no non kosher animals milked locally, was served milk mixed with animal brains, and exhorts people to be careful with divrei Chazal.
As to your point- the Chasam Sofer makes mention of this in his famous psak where he says Chalav Stam is totally assur afilu batul ta’am lo batul gezeira. He makes note of the fact that most of Kehilas Ashkenaz is (was then) noheg lehachmir, and says if you hold like him it’s assur derabanan and sfeiko lekula, but if are in Kehilas Ashkenaz and you hold like the Pri Chadash it’s considered a neder and it’s assur min hatorah so sfeiko lechumra! (I just want to point out though that several friends of mine learned by R’ Nota Greenblatt in Tennessee and he told them beshem R’ Moshe they don’t need to be matir neder to drink CS in Memphis as their whole hakpada on CY was based on the fact that they live in town).
I have heard some opine that R’ Moshe was giving an after the fact heter based on the observable fact that most Americans drank CS, and therefore it was minhag hamakom to rely on the PC.If you’d like I can try to write up a basic summary of CY- from the Gemara down to modern day poskim based on the Shivti marei mekomos. It’s a relatively short contained sugya.
Chasam sofer and chochmas Odom both hold it's davar shebiminyan but seemingly not the same gezeirah.
The chazon ish problems with the Chasam sofer don't seem to apply to the chochmas Odom. Chasam sofer seems to say it's din re'iyah which is difficult for a variety of reasons, first and foremost the Gemara by ain davar tamei b'edro. The chochmas Odom seems to say that the gezeirah is to be choshesh for a chashash rachok
