The 1920 U.S. Census states that my great grandfather came over to the U.S. in 1903, and was naturalized in 1907. This checks out, because the 1907 naturalization laws of the U.S. state that the person seeking citizenship has to have lived continuously in the U.S. for at least five years.
However, I also found a border crossing (from Canada to the U.S.) document . . . I know the man on that document is my great grandfather -- he has the same name, same birth date, lived in the exact same town in England, etc., etc. So I know that it's him on that border crossing document!
The problem is that the document is from May 1907 . . . and supposedly my great grandfather had been living in the U.S. for a continuous five years by then. Hmm.
What does this all mean? Which document is correct?