Thank you for your response. The microfilm for this ship manifest was created in 1944 -- which explains why neither of us can see any cerificate of arrival markings on it after the early 1940s. I don't know whether this means that in producing later certificates of arrival, they just looked at the microfilm for verification, or if they still marked up the original manifest.
Thank you for the excellent suggestion that I contact Marian Smith. I will do so.