Even Common Surnames get Misspelled

While researching a family with a common surname in the federal censuses yesterday, they remained in the same county and town in Illinois for forty years, unlike some of my ancestors with gypsy feet gone somewhere else further west EVERY census! While I found them easily in the 1870 and the 1900 Lee County census as Jones, I couldn't find ANY of the family members in 1880, which has been thoroughly indexed. My decision was to go page by page in the town that I had found them in both sides of this census and on pages five and six, there they were but the surname was unmistakably spelled James. Everything else matched perfectly!

Now I have a theory here (as I am wont to do in these matters), since the son's name was James, could the census taker have just been tired/careless in writing the surname? Or was this a duplicate copy and proper care wasn't taken in handcopying all of the entries and non one caught the error when checking for accuracy? The main purpose of the census was to get an accurate count of population after all, for the House of Representatives apportionment, not the specifics of each family, although genealogists are certainly happy about the increased detail the federal government desired on subsequent censuses . We've all had those moments where our brain seems ahead of our hand and while I will never know for certain, I was grateful to have found them.