This is from a book titled "Guide To Naturalization Records of the United States" by Christina K. Schaefer.p.9
"Census and Mortality Schedules"
Certian Census Schedules give specific information that can pinpoint a time of immigration and indicate if a pereson was naturalized. The 1900, 1910 and 1920 censuses are soundexed by state. There are codes on the soundex cards that give specific naturalization information:
Pa - papers, immigrant has petitioned the court of citizenship
Na - immigrant is a naturalized citizen
Al - alien
NR - not reported "
It then goes on to give more information and I could type all day, but my point was that first this information is only found on the Soundex card for the above census, so check them too, and also to point on the Na status, I
assumed it meant Not Available or Not applicable for my ancestor, when in fact it means Naturalized. So i just found another clue about my ancestor that I already had ! Back to the hunt ! (I do not own this book, found it at my local library, lots of good info in it though)