I've been trying to work out what June 19 is all about. From what I'm gathering, it just appears to have been a random date at the start, that they just chose for no reason. However, people noticed, and so they started adding it in more, without an actual reason.
Of course, they don't have a reason, so we can make up our own! The consensus is that it's the day they were kidnapped, and forced to start learning things. Maybe they were all brainwashed, and their bodies had surgery to change into these, and that's why there's so much flesh.
Hmm. Maybe not. Still, it's fun to think about.