Are there more than 12 golden keys in Fairy Tail? I think that the King of the Underworld Mard Geer and the Celestial Spirit King fight more than 1 fights because in episode 249 Mard Geer said to the Celestial Spirit King "I don't believe I will lose to you this time, either."



but it's impossible for Mard Geer to go to the Celestial World, so I believe that a golden key or more was destroyed before Aquarius.

Are there more than 12 golden keys?
The Keys regenerate in time. This is confirmed early on into the final major arc of the manga, which has yet to start in the rebooted Fairy Tail Final Season Anime, but this is minor spoilers

https://fairytail.fandom.com/wiki/Aquarius in the Alvarez Empire Arc


  A year later, Aquarius reappears (of her own accord) from a spilled vase of water, saving Lucy from the wrath of (Spoiler)....Aquarius then proceeds to happily embrace Lucy, and explains that another Water Bearer key has surfaced somewhere in the world, and that the Celestial Spirit King opened her gate temporarily, which allowed her to save her


So its likely that someone did sacrifice the key to summon him, and then later on the key regenerated and reentered circulation.