As far as I know, all 74-77 c-bodies had a label on the top of the driver visor (against the headliner in the stowed position), and never a label on the passenger visor.
76 visors are a different shape than 74. Top to bottom: driver visors for: 74, 74, 76:
The label on a 76 talks about catalytic converters, while the 74 doesn't. Top to bottom: driver visors 74, 76: