Thank you for your very helpful reply.
Based on his year of naturalization (1945), your suggestion is to obtain his file by requesting his “USCIS Certificate File (C-file), available also from USCIS Genealogy Program.”
What reference number should I use in the request?
I also have a copy of the naturalization index card which has nothing in the “Alien Registration No. blank” but does have an A.R.# typed in below.
Do you know if there is typically additional information in the C file besides the main forms?
Arrival in 1912, naturalization 1945
Annotation on manifest for CA is 1939.
Certificate of Arrival – actually a Certificate of Registry (stamped on his CA)– Form N-225 – 18 Sep 1942
Declaration – 25 Oct 1942
Naturalization certificate issued – 20 Nov 1945