99% of all vinyls only stretch in one direction, what is called two-way stretch. It may be laid out on the roll so that it stretches from top to bottom on the roll or from side to side on the roll, but it still only stretches in one direction. The vinyls that stretch in two directions ( four way stretch) are very limited in color and grain and are intended for things like ATV seats, jet ski seats, etc. Car seats have been made with two way stretch vinyl forever. If your seats are not turning out correctly, there is something else wrong that has nothing to do with the vinyl. Most upholsterers will tell you that too much stretch, and especially in all directions, is as bad or worse than not enough stretch.
No one lives forever, the trick is creating something that will.