Every single one of those examples you cite (since 1976) are due to extentuating circumstances that have nothing to do with how good a team is.I have said it on here multiple times, only 4 teams (3 programs) since 1976 have won back-to-back national championships and it wasn't because all those other teams didn't have talent. Its an almost impossible task in sports.....(except basketball). Especially in college football. Team Turnover, Staff turnover, Injury luck, Schedule luck and team chemistry have to be almost perfect two years in a row.
1978-79 Alabama - only happened because there were two polls
1994-95 Nebraska - may have only happened because they could avoid playing the #2 team
2003-04 USC - only happened because of a revolt in the AP poll
2011-12 Alabama - only happened because Ohio St was on probation
The closest we've had is Alabama leading Clemson until Pick Play II to end the 2016 season.