This isn't a particularly huge mystery by any means but there does seem to be some confusion as to whether or not all 14 episodes of Planet of the Apes were broadcast in 1974 on CBS. The live-action series, which starred Roddy McDowall, Ron Harper and James Naughton, premiered on Friday, September 13th, 1974 and was off the air by the end of December. Harper and Naughton played Alan Virdon and Pete Burke, respectively, astronauts flung far into the future into a world populated by apes who find themselves fugitives. McDowall, who appeared in four of the five Planet of the Apes movies, played a chimpanzee named Galen who befriended the humans. The episode that some sources, including the 2001 DVD release, say was unaired is called "The Liberator" and saw Virdon and Burke captured by a village of humans.
The sources that state "The Liberator" was never aired say that another episode, "Up Above the World So High," was broadcast on Friday, December 6th and was the last first-run episode to air. Other sources insist that "The Liberator" aired on December 6th and "Up Above the World So High" on December 20th. Here's what weekly and daily television listings from a variety of newspapers have to say:
- Weekly listings published on Sunday, December 1st indicate that "Up Above the World So High" was scheduled for Friday, December 6th. Daily listings confirm this.
- Weekly listings published on Sunday, December 8th indicate that Planet of the Apes would be pre-empted on Friday, December 13th for holiday specials. Daily listings confirm this.
- Weekly listings published on Sunday, December 15th indicate that "Up Above the World So High" was scheduled for Friday, December 20th. Daily listings confirm this.
- Weekly listings published on Sunday, December 22nd indicate that the premiere episode, "Escape from Tomorrow," was repeated on Friday, December 27th. Daily listings confirm this.
Based on this information, it seems that "Up Above the World So High" was supposed to air on Friday, December 6th but for some reason was not shown until Friday, December 20th. Unfortunately, there's no way of knowing what actually aired on Friday, December 6th looking only at printed television listings. It could have been replaced by "The Liberator" or it may have been pre-empted entirely. Short of checking the logs of a CBS affiliate or the network itself, or perhaps a diary entry recounting what someone watched on the evening of December 6th, I can't think of any other way to confirm what CBS broadcast on December 6th. In this case, television listings are simply not enough to go on.