When singing the lyrics to "Fate's Wide Wheel", "close" is mispronounced as an adjective (klohs: being in or having proximity) when it should be pronounced as a verb (klohz: to come together, unite) to rhyme with "goes" (gohz). This error is also on the soundtrack CD.
Just before the last gig, the bassist of the band is adjusting a new green wig, claiming his own - which was blond-colored - had been stolen. However, he was already wearing the green wig during the previous concert when performing "Rock the Redhead", which shows that the two performances were, in fact, recorded on the same occasion.
When Sam and the band are leaving the concert in a limousine, a FOX body Mustang can clearly be seen in the parking lot. The FOX body Mustang first appeared in 1979, though the episode is set in April 1974.
Leaving the arena, the close-up limo could have been 1974, but also 1975 or 1976. But the far shot was definitely a 1980 or later. This episode takes place in 1974.
In the sequence where Sam is waylaid in his hotel room by the three young fans, the television set is playing the news. Once he has rid himself of them and is talking to Al, we still hear the television playing in the background, however, as the camera pans across the room, the TV is turned off.