But Bob has -1 gold coin in his bank account, so there is still only 1 gold coin. If Alice deposits her "new" gold coin into her account, the bank still has only one coin. If Alice demands to withdraw her 2 coins, the gold bank won't be able to comply, whereas the fiat bank would just print another coin.
That's not how amount of money is calculated. If you did, you would end up with a funny result that there is no money at all. As all modern money is debt from someone to someone else.
