Post any and all teams you feel got slighted.
I don't feel an undefeated G5 being passed over for a 1-loss P5 qualifies, sorry.
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Some examples:
2004 Auburn (undefeated, but behind USC and OU)
2011 Oklahoma State (1-loss, passed over for 1-loss Alabama's rematch with LSU)
2007 Kansas (1-loss, ranked behind six different 2-loss teams, in the season of crazy)
2008 Texas (ranked behind OU, despite having h2h, in 3-way tie for XII South)
2003 USC (ranked #1 by AP, left out of BCSCG)
2000 Miami (ranked behind FSU, despite having won h2h)
1994 Penn St (undefeated season, no split NC)
1993 West Virginia (2004 Auburn situation)
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A lot of teams that were on probation could have a gripe (12 OSU, 93 Auburn, 84 Florida, etc), but since they were on probation, the voters punished them and ho-hum. That's how it goes.
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1992 Texas A&M (undefeated regular season, ignored)
1987 Syracuse (same as 92 A&M)
1983 Auburn (ranked 3rd going into bowls, 1 & 2 lost, but didn't win the NC)
1982 SMU (left out due to a tie, fell behind teams with a loss)
1977 Alabama (see 83 Auburn)
1976 Maryland (undefeated regular season, ranked behind two 1-loss teams, no chance at NC)
1966 Alabama (won previous 2 NCs, ranked 3rd despite going undefeated)
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I'm sure there's more, but which ones did I miss??