Near the end of Final Fantasy X it is revealed that:
Lord Zaon was the first final Aeon forged by the bond between him and Lady Yunalesca. The old man in Zanarkand says roughly: "The final Aeon can no longer be summoned. [Zaon]'s soul is gone."
I assume, that for some time summoners could use the Aeon produced by Lord Zaons fayth to fight Sin, but no longer, which is the reason that summoners must sacrifice one of their guardians to aquire their own final Aeon.
It is also said, that this final Aeon, if it defeats Sin, becomes Sin itself. So if all of that is true, then how could a final Aeon be used multiple times? If it defeats Sin it disappears.
But apparently Lady Yunalesca, who was the first to defeat Sin, used a final Aeon other summoners were also able to use for some time, afterwards.
Is that poor word choice and
Lord Zaons Aeon was also only used this one time
or is that an inconsistency in the rules?