There's usually something that slips, the day before or day of. Usually because of photos from the convention center being set up or some dummy hitting a button early. Mario Maker was found out last year from demo stations, and SFV was discovered before PSX because someone in charge of the Capcom youtube channel made the trailer public early. So basically if you want to be surprised avoid neogaf and the internet for that matter the day or two before the show.
Also the internet has become really good at tracking down trademarks and that should start happening sometime this week.