More than 100% turnout?

This isn't the most sophisticated way of looking at things, but I've been matching up census data with city level voting data.

The census gives a year-by-year age breakdown, so I've conservatively estimate turnout by counting the entire population over the age of 15(The voting age is 18, and the census is 3 years old), and assuming no mortality.

So far, I've only looked at the 10 subdivisions in the Province Yazd, and three provinces stand out with suspiciously high turnout. Saduq(صدوق ), Mehriz(مهريز) , and Taft(تفت) , with 97%, 104%, and 130% turnout respectively. Excluding those provinces, the average turnout was 77%.

Perhaps there is an innocent explanation (Immigration or Migratory workers?), but it warrents explanation. I'll expand the analysis to other provinces and see if the result holds.

Update: See Nate Silver