As already stated, shoulder belts were mandated on Jan. 1 1968, but they were optional before that. My 68 Charger was built on Dec. 15, 1967 and it had the optional shoulder belts. I have seen a lot of 68 cars that were built before Jan 1, and they have a hole in the roof, but I have never seen one that had the threaded insert unless it had the belts. The Chrysler corp. would have been in violation of federal law to build a car after Jan 1 1968 without shoulder belts, so I think it's a safe bet that the headliner had been replaced in the car that this post is about.