Joseph: “Gaon: Are you arguing that Rav Moshe’s Psak against an Eruv in Manhattan or Brooklyn would be applied by Rav Moshe to Radun and Mir as well?”
First of all, lets establish that Rav Moshe accepted the tenai of shishim ribo lechatchila.
You missed his point. Once a road is 16 amos wide you either rely on the criterion of shishim ribo and you can establish an eruv, or you don’t rely on the criterion, and an eruv can’t be made (if there is no other heter) even if its a tiny shtetl.
“YDS: Psak Halacha doesn’t work by counting (for majority or what not) seforim/sh”ut that were long lost but recently found, but were not considered by the corpus of responsa by the gedolei poskim of the intervening centuries.”
First of all, you are mistaken regarding recently found poskim. We accept their opinion as long as it does not overturn established halachah/minhag. In fact this is our argument, shishim ribo is the accepted minhag.
You missed the point. It was the MB/MY who argued that the majority of poskim opposed the criterion of shishim ribo. So by their own argument if we now know that the majority does uphold the criterion of course we can rely on it. But, if we follow the minhag then there is no doubt that we rely on shishim ribo.