Since you are so greatly interested and would be comfortable with non-Chinese-language documents, may I suggest you purchase some of the very interesting history publications by your compatriot and highly esteemed researcher Erik van Ingen Schenau, who is, as you must know by now, a member of this forum. These may perhaps help to fill the gaps in knowledge that you might have regarding this industry. His general catalogs (extensive and exhaustive) are no longer for sale, unfortunately.
https://www.chinesecars.net/category/catalogue/history-documents
https://www.chinesecars.net/category/catalogue/history-documents