I know - when I purchased the car on 1 Nov 1991, the standard interior seats were in the car. I've obviously had both the front buckets as well as the rear bench out of the car on multiple occasions. The seat covering materials looked like it has been there for a very long time. If you didn't know better when you looked at the bottom of the bucket and bench seats as well as the back of the rear bench seat you'd say they had been there from day one.
I considered changing them, but since this is the way the seats were when I got the car, I left them as acquired.
The rear bench seat still has the "original to me" standard interior seat material, as it was, when I purchased the car in Nov 1991.
The first picture below, from May 1992, shows the front bucket seats and material (standard interior), as they were when I purchased the car. Due to wear through near the seat belt retainer, I had the front bucket seats recovered in late 2013.
The 2nd picture below is from April 2014. The front bench seats have been recovered. The rear bench seat has not been recovered - still in "original to me" condition; i.e. as it was, with the same material, when I purchased the car.
Third picture is my trim tag. Car was originally Dover White with a Dark Blue Vinyl top. When I purchased the car, the vinyl top had been removed and the car had been repainted.
Who knows how or when much less why standard interior seats wound up in a custom interior car. After all these years of owning the car with the interior as displayed, it is a moot point to me.
Richard