Where did you check that?
There is erroneous and conflicting information on when Spiro Angew dad was naturalized. It has been posted on FR and around the Internet. I’m going to find it now.
Checked at post 89 too:
"1930 census, Line 65, Angew's father was naturalized in "1903 Na." Spiro Agnew was a natural born citizen. "
http://www.freerepublic.com/focus/news/2703612/posts?page=89#89