These photos of John and very pregnant Yoko have been in my files for a very long time. I recently discovered the People magazine with the top photo that had a caption that stated that it was from the New York Film Festival.
So I looked up information on the 1975 New York film Festival and discovered that it took place in October of 1975. That means that these have to be the last photos of John and Yoko taken before Sean's birth on October 9.