1) How do you know what Rav Moshe was lead to believe? He quotes a ‘city map’. If you know the map to have been fraudulent, then say so. (And then produce the map. Or something like that.) If your deducing from some inconsistencies, that Rav Moshe was mislead, I’ll explain them to you for the benefit of the audience. Anyone who thinks they can outthink Rav Moshe because they can’t fit all the pieces of his teshuva together, is obviously stupid. If the ‘city map’ was accurate then he wasn’t misled. Rav Dovid Feinstein wrote that his father was told 2.5 million which is on par with census. Rav Moshe starts the Flatbush teshuva with the number 600K in the ‘streets’. What does this mean? (Some of the mattirim say in the streets of the eiruv. It doesn’t read well and Rav Moshe rejects that shitah in a different teshuva.) The inference of the whole teshuva is that Brooklyn is more than 12 mil and that there are ways different ways to measure it. Rav Moshe explains at one point why parts of Manhattan should not be counted in Brooklyn. Rav Moshe also says it wouldn’t need to be every day of the they year. It’s a very vague teshuva in terms of statistics.
One of the mattirim (Boro Park Eiruv) told me that if Rav Moshe would have written it slightly differently he would assur. as if Rav Moshe was writing the teshuva for his benefit only. When you learn a teshuva you are supposed to consider the writer’s opinion and forget your own.