Were copies made of the census?

I have a copy of a census page, Kewaunee County Wisconsin, that I inherited from my mother. While it is mostly the same, and has the same census taker's name, date, etc. there are differences in the information between that page and the one that shows on Ancestry.com. My ancestor is listed as 24 years old on Ancestry, and 23 on the copy from my mom, and his occupation is listed on one, but not the other. It's absolutely odd.

I'm wondering if anyone has experienced this as well and could shed any history on it.


Thanks

As I understand it, once the census was done, a copy was made so that there was a copy for the state and one for federal. I imagine errors in transcription were bound to occur.