Flatbush and Boro Park
Flatbush and Boro Park were the subjects of specific Brooklyn eruv proposals and responsa. They form part of the same large-city background relevant to Crown Heights.
Rav Moshe rejected the report of a Flatbush heter
Igros Moshe Orach Chaim IV:87 answers a report that Rav Moshe had permitted the Flatbush eruv. He corrects that impression and makes clear that no such permission had been given.
Orach Chaim IV:88 develops the Brooklyn analysis further, addressing the citywide setting rather than treating Flatbush as a separate small town.
Boro Park and the later Brooklyn discussion
The Boro Park controversy again raised reshus harabim, shishim ribo, the proposed boundary, and the use of Rav Moshe's earlier words. Orach Chaim V:28 returns to those large-city questions.
Rav Moshe also discusses the effect of public carrying on visitors and on people from communities where no eruv can be relied upon. A neighborhood practice can teach far beyond its borders.
The public rulings of 5739
The Kislev proclamation repeated the Manhattan prohibition and applied it to New York and other large cities. Rav Moshe's signed letter of 17 Teves again opposed establishing the proposed Brooklyn eruv.
A further notice carried the names of seventy-three Rabbonim from numerous communities. The public warning extended across New York communities and beyond a single neighborhood.
The relevance to Crown Heights
Crown Heights lies within the same Brooklyn street network considered in these rulings. The large-city questions cannot be avoided by placing the route inside a different neighborhood name.
Its Beis Din later issued a direct local psak prohibiting reliance on the advertised eruv.