We're talking about the 1969 season. That year the Coaches' Poll completed its final voting in early December, before the bowl season, and 10-0 Texas was voted #1 while 10-0 Penn State was voted #2. The AP Poll completed its final voting in January after the bowls, and 11-0 Texas voted #1 while 11-0 Penn State was voted #2. Had Penn State accepted the Cotton Bowl invitation and beaten Texas in Dallas, then it's presumed (and highly likely) that they would have won the AP Poll vote for #1. I don't know about any of the other rankings, the AP and Coaches' polls are really the only two that mattered at the time and they're the only two that matter still.
Despite the popular myth, Nixon awarding Texas the "national championship" via a small plaque he had made up, after the Texas-Arkansas game, really had nothing to do with the actual national championship. The voters in both polls were still free to vote for whichever teams they saw fit.
Then it was the following year, the regular season for 1970, where the polls were split and Texas was voted #1 by the Coaches' Poll at the end of the regular season, while Nebraska was voted #1 by the AP Poll after the bowl games (Texas finished #3 in the AP that year).
This Georgia football talk is fun!