Just the five from the major selectors. We have arguably the best claim to all of the five official titles we claim, and while we could claim others, there are better arguments for other teams than Nebraska. The stretch from 1980-1984 would be silly to claim titles from, for example. However, give us a playoff in those years and I'll bet Nebraska gets at least one title in that span. Lots of things change in a playoff. You get more film, players get banged up, etc.
I don't understand how anyone could have chosen Nebraska in 1983 or 1993. We lost both of those on the field. Those are no-brainers.