The official source is Sonic's announcement video that can be found the official website's offical YouTube page which Sakurai himself officially released. I'd say that that's official enough until Sakurai announces anything that reflects the contrary.
How do you know those are the controller inputs for those attacks? If you don't know the controller inputs you can't list the attacks. And how do you know the official title is that anyway? The game's logo has the words "for Wii U" and "for Nintendo 3DS".
Because thus far nothing has changed for Sonic. And his downswipe wouldn't be an up normal attack. A lot of it is common sense + some knowledge of how Sakurai operates. Plus I even stated on the page up top that his moves so far have remained unchanged, at least the ones they've showcased. This Wiki is as much speculation as it is proven facts.
You can't use common sense, deductive reasoning, and the moveset used from Brawl to make these kinds of conclusions. If an aerial attack hits upward, there's absolutely nothing preventing that attack from being a down aerial instead of an up aerial. The definition of an up aerial is "an attack performed by pressing the attack button along with up on the Control Stick while in the air", not "an aerial attack that hits above the user", etc. If you see Sonic using what looks like a forward aerial, there's no reason why it can't be a back aerial. Moves from previous games have also changed their inputs; look at moves like Mario's Down B in Melee to his down aerial in Brawl, or Captain Falcon's forward aerial in Smash 64 to his neutral aerial in Melee.
"This Wiki is as much speculation as it is proven facts".
No it's not, speculation should not be on this wiki, and claims that require evidence should not be listed when no evidence can be given to support those claims. We can't give people the impression that something is true when it may not be.
To an extent I can see what you're saying and would agree that wild speculation shouldn't be used. However, I'd say that based on the video it's more than an educated guess. If we're throwing common sense completely out of the window then I can go along with what you're saying. In the video Sonic uses enough moves to make a very educated guess. And if something winds up changing it can always be adjusted. I see your point, I do, how do we find a common ground?
Why should we add them if we aren't 100% sure anyways? As I already told you, speculation is not acceptable, control inputs can change across games, and what you think something looks like is not always what it actually is. You could be wrong if you add the moves by using common sense and that is not okay here.