This should probably be in another forum, but I don't know which one, so I am answering it.
The word "stock" meant inventory originally. Stock still means inventory for a store.
In Amsterdam, there were joint ventures where different vendors brought different inventory to a store. They received a certificate showing that they owned a certain amount of inventory (stock) at the store. The retail store then sold an item belonging to some inventory owner, they received money and the certificate was exchanged for a corrected version. That would also be true if more inventory were added.
Stock was not fixed. It varied as different vendors contributed inventory. Of course, in practice, inventories were roughly stable. It also was observed that somebody could really just contribute money and the store owner could buy the materials from someone that didn't want to contribute to the inventory.
A joint stock company with fixed capital is the next iteration. Unlike a traditional partnership, it could survive the death of an owner. After all, if I had contributed 100 candles, my death only passed ownership to my estate for my claims on the candles. Likewise, if I had a claim on candles, I could pledge them or sell them to somebody else.
Like a partnership, joint stock companies do not provide any immunity to shareholders from any lawsuits. That is still true today. Very few joint stock companies still survive to this day, but they do exist. The largest one that had been a joint stock company was American Express. However, a lawsuit scared the shareholders and they converted to a traditional corporation once it was settled.
It is not true that the Amsterdam exchange differed only in technologies. Old exchanges did not use double auctions. The double auction, where buyers bid against buyers and sellers bid against sellers, is relatively new.
The Amsterdam Exchange traded other things than just the one joint stock company at that time. It was a general commodified asset exchange.