The introductory paragraphs for the First Day Cover section of the Scott U.S. specialized catalog states the cities listed are those officially designated by the Post Office Department. The catalog doesn't state these are the only cities that applied first day cancels.
The U.S. Receiving Ship at the Brooklyn Navy Yard seems to have applied an unofficial first day cancel.
My take on this cover.
Robert
By the way: The U.S. Receiving Ship at New York during this time was the former USS Washington (ACR-11).
https://en.wikipedia.org/wiki/USS_W...ton_(ACR-11)