I'd like to have a good look at the front of the arm rest, next to the door, from the front and from the outside. On my roadster the left side and the right side are different, and they may both be wrong.
There are some good pics in these threads:
Let's see what you've got.
From what I know from different threads on the subject concerning upholstery on this model year range and the range of the 17-22 year range on open cars that I own I don't know if you can pin it down exactly.
Maybe the upholstery installers didn't always stick with exactly the same installation techniques since it was done by hand exclusively.
Keith, it will have to wait. My digital camera is out for repair.