The cloth is different.
The original cloth had multiple colored threads making up the tweed(cloth). As you know it kinda had the look of a flannel shirt. LOL
The tweed (cloth) used on the TMI seat covers only uses one or two colored threads making the tweed.
Its more of a solid color. My '88 vert has OEM cloth panels integrated in the door panels above the handles. That cloth is slightly different than what was used on the seats.
The TMI cloth tends to match that panel almost perfect.