There were 2 different mthods used. Seems like cars through 81 had a vinyl strip around the perimeter, with metal "clamps" at the ends. The later ones were hemmed as previous;y described, then stitched together around the perimeter.
FWIW, when I did the coupe headliner/visors, i did the fabric myself, and asked the trim guy we use at work about doing the edge vinyl (which I had) and he wanted $125. Repros were less than that. I wound up getting in touch with a woman locally through my in-laws who did them and wanted $15. We paid her $35. She wound up doing my seats as well. since none of the presewn covers were the correct color.