If a Company is closed, ALL Share Certificates should be in the CLOSED Portfolio of the Bank (to allow undo), and NEVER be added to the IPO Portfolio of the bank. And regardless of the location, the Bank should never show Certificates for closed company where they can be purchased again.
When the game is saved (via auto-save or specific save action selected) the Bank's Closed Portfolio is now saved. When it is loaded, this will be reloaded.
If a Company is closed, ALL Share Certificates should be in the CLOSED Portfolio of the Bank (to allow undo), and NEVER be added to the IPO Portfolio of the bank. And regardless of the location, the Bank should never show Certificates for closed company where they can be purchased again.