Mr. Head said:
WKRP in Cincinnati had a couple of continuity errors.
In one episode during the first season, Les Nessman goes to Carlson and demands a raise, arguing that he had been with the station for seven years without ever having gotten one. Since the show started in 1978 and took place in the then-present time, this would indicate that Les had only been employed at WKRP since 1971. However, in a later flashback episode, as a spoof of A Christmas Carol, Carlson is taken back to 1955, and among the characters employed at the station back then is a young, squeaky-voiced Les Nessman (with a full head of hair as well). The then-general manger gives the young Les a bowtie as a Christmas gift and promotes him to "a full-blown cub reporter", to which Les responds, "You'll never see me without a tie again."
Also, in the first season, there is an episode where it is revealed that Venus Flytrap is an army deserter, and that his real name is Gordon Sims. In this episode, nobody, not even Venus' longtime friend Andy Travis, knew Venus' real name until he revealed it in this episode. However, in the fourth season, in a flashback scene to the night Venus first arrived in Cincinnati, he and Andy are shown at Andy's home talking, and Andy calls Venus "Gordon" as if he had known his real name all along.