Maybe he didn’t know what year he was born, or maybe there is some other functional reason. Are there ways of categorizing the documents by date signed or what the document was for?
I have to apologize to Elendur. I didn't read his comment closely enough. He pointed out that prior to 1962, all Barack Sr.'s documents used the 1934 birth date, but after 1962, Barack Sr.'s documents used the 1936 birth date. A quick examination of the immigration files seems to confirm that. I didn't do a thorough one, but a quick check seems to hold with his statement.