Shark skin is more like added by later generations, and the explanation is that fish skin is more reasonable.
The earliest record I can find is in Song Dynasty Mei Yaochen's "Answers to the State's Relics of Sharks and Fish Skins", which mentions shark skins made from shark skins! Of course I found it on Baidu, I guess there was a big mistake, but trying to find the history of shark fishing in so many ancient books seems a bit overwhelming! My personal understanding is that shipbuilding in the pre-Qin period was underdeveloped and insufficient to support shark fishing in the open sea!