If you're referring to the physical cockpit jumpseat, you're correct. However, most airlines will allow pilots to use their jumpseat privileges to occupy an empty seat in the cabin.

With AA on international flights, that courtesy is only extended to a very limited number of airlines. If you're not on their international jumpseat list, AA will not take you even if there are 100 seats open in the back. This is unlike DL, UA, CO, US, etc. who will allow you to "jumpseat" in a passenger seat on an international flight.

So, the short answer is if you fly for an airline that's not on AA's international jumpseat list, the only way you'll be able to get on an AA international flight is to buy a ticket or an ID90/Zed fare.