I have two Corbin seats. I'm pretty certain when ordering the first one that they recommend leather for the surface we sit on, but use a man-made material for the rest of the covering, as it is more durable and copes better with us squashing it while seated - it recovers better. Whether it is actually vinyl I don't recall. It does however need more attention, to keep it looking similar to the leather, but mine has survived almost 15 years and is still going strong.
Just to add and you may already know this, custom stitching looks nice, but the more the stitching the more water will get in when out in the rain. Big deal probably not.