I'm interested in learning a little more about GM's Comfort Clip...a plastic devise that was attached to, and slid on, the shoulder strap, thus allowing the passenger to adjust the tension of the upper shoulder strap. What year were they first introduced? Were there different styles for different models, i.e., Corvette, Camaro...? What about different methods of attaching the clip to the strap? I've recently acquired a few of these clips...some of which consist only of the clear plastic devise with the white lettering "CAUTION...etc., etc.", while some of the others have another plastic piece, faded off-white in color, that fits inside the back part of the clip. When attached, you can see what looks like 3 vertical slats. I've attached both clips to a strap and find no difference in their resistance to hold a position when slid up and down. Is anyone more familar with their history and application? These clips were accompanied by a specific instruction sheet...the one application I'm familar with them on is for my '74 Coupe. Any further information or insights...would be appreciated. Thanks.