I'm guessing that at least 12 are handed out. With the rise and spread of three and four receiver sets on offense, a nickel back can essentially be labeled as a starter now. Nebraska plays multiple teams this year that run "spread offenses."
Based off of what opponents ran last year/new head coaches, it's possible that the Blackshirts are rarely in a base 3-4 against Oregon, Ohio State, Purdue, Penn State and Minnesota. Then they'll probably use the 3-4 almost exclusively against Wisconsin and Iowa.