Actually, the big difference was how they handled the seams. On a non-vinyl top car they leaded the seam which held up great. On the vinyl top cars they used a kind of plastic filler that often bubbled up. Just another example of early cost cutting which resulted in less quality. I can't tell if your car has the filler and I don't see any bubbles. I remember looking at an FJ6 AAR back in 1984 that was for sale in my area with only 5k miles on it. It was a former race car and had beautiful original paint but I always remember seeing those bubbles under the vinyl top at the seam. A shame.