User blog comment:FairyRaven/Fairy Tail Chapter 337: The Golden Plains, Review and Commentary/@comment-112.198.249.25-20130629134349/@comment-7418318-20130630093957

What makes you think the Dragons forgot? Tell me even a single hint in that direction.

The only hint about the Dragons remembering this mini-invasion or not is Zirconis seemingly getting the idea for his nickname "Jade Dragon" from Hisui, which suggests that the Dragons do remember.

We have not a single hint that would suggest that any of the Dragons forgot anything. And any gaps in Zirconis' memory, when Wendy calls his soul with milky way are far more likely the result of spending the last 400 years decomposing to the point where he just vanished in the middle of the conversation.

Though looking back, it might be possible he didn't disappear by himself. He just said "Because of you..." when it happened, so it might be possible he might have told them about the 7 Dragons invading, but someone or something intervened to make sure he couldn't do that.

As for Mavis, having her act as the comical relieve would make the revelation that she's actually the master manipulator behind the scenes (no matter if it's for good or evil ends) all that more delicous.

I was very surprised when that "bumbling brat" suddenly turned out to be a master tactician.... only to have that appearance undermined by breaking down in tears because she failed to predict Kagura's actions. But maybe that was just pulling the disguise of being harmless back in place, after revealing a bit of her true abilities out of necessity.