I'm starting to doubt these being slip ups. Honestly, these leaks are too... I dunno. It feels like they're on purpose. I mean, the beta Anime artwork comes out, then we get more info on Koromori (legit source) and the little one-horned thing from a questionable source? There have been a LOT of 'slip ups' if that's what they are. Either the Pokemon company is really lax this gen when it comes to security, or they're purposely letting small details through the cracks to keep the rabid fanbase entertained.
I mean, think of it this way. This way, they don't have to shove every single detail into CoroCoro/Pokemon Sunday/Oha Suta. They get the publicity as everyone eagerly awaits confirmation, they get a more focused fanbase. If they did like they usually do, shove the bulk of information in CoroCoro, with some nifty moving images called 'video' and maybe a new unimportant tidbit on PS, you can just feel the cycle of anticipation.