For example, in the United States, Federal Motor Vehicle Safety Standards (FMVSS) generally require cars manufactured after a certain date to have factory-installed seatbelts at specific seating positions. However, some states have exemptions, modifications, or grandfather clauses for classic cars or vehicles that meet specified conditions or age criteria. Check the local transportation or motor vehicle regulations in your jurisdiction for specific rules for classic cars.
It's important to note that these requirements can vary and evolve over time, so the best course of action is to refer to your local legislation, or consult with transportation or government entities responsible for vehicle laws in your area.