If your question is "In what year did Shoulder Seat Belts become mandatory in cars sold in America?" -
In 1967, the National Transportation Safety Board issued Federal Motor Vehicle Safety Standard 208 (effective 1/1/68), which required auto manufacturers to install lap and shoulder belts in outboard positions (next to windows) and lap belts in all other positions.
The first mandatory shoulder belts were not the 3-point belts as we see nowadays. They were just a belt attached to the inside roofline of the car, and there were no retracting rollers to coil them up neatly. There werea couple of little chrome "paper-clips" to hold them up above the door line.... otherwise they just dangled. They were a hassle and people hated them. The ones in my 69 Camaro stayed exactly where the factory had installed them until the day I sold the car.