User blog comment:FairyRaven/Fairy Tail Chapter 391: Gray vs. Silver, Review and Commentary/@comment-24784846-20140704210129/@comment-7418318-20140705230539

Sure it's possible, but if that was the case then Mard would have to either rename the former Eight Demon Gates into the Nine Demon Gates or demote one of the Gates to make room for Silver.

Unless that one member somehow got itself killed in a way that made Mard so angry that he refused to let it be revived or made it impossible.

And I'd really like to know which of those possibilities it was.