the absence of any sort of rumor of actual games apart very few is emblematic of the situation
many insiders confirmed that the situation is just in terms of discussion, no actual games in firm development position
the march release is officially due to lack of software (with nintendo internal development freezed on 3ds or wiiu...that picture a very barren situation for third party support)
we can imagine a different situation for indie and Japanese softco, but western third parties will not be there at launch and even for the fall '17 I am pessimistic
you say we should take in consideration also positive rumors but the actual game-related rumors are just DQX, DQXI, Koei officially at work on something. those are from Japan.
indie games lire Rise and a couple more.
the only western ones are two from Ubisoft I think. Beyond good and evil 2 and a "beta tested" one
So we have 2 rumored western games, 1 backtracked indie game, 2 backtracked JP games, multiple rumored Bandai Namco games, 1 of which is likely Smash, and Koei confirmation that they're doing something. That's at least 7 rumored third party games (6 not counting Smash I suppose) not counting anything from Koei Tecmo. I'm sure I'm missing some rumors too.
On the other side, we have a handful of developers saying they don't know anything about the NX. We have Toys for Bob, Ready at Dawn, Thomas Mahler... who else? I'm sure there are more, but the general theme of this point is that they aren't big publishers, they are generally small to medium sized developers.
For better or worse, Nintendo typically doesn't approach these types of teams directly before a console launch. See the Wii U- they were in direct talks with EA, Ubisoft and Activision and they got several games from each of them around the launch window. The development teams who made those games likely didn't have much info before the console was revealed, yet the games were still made.
The point is, just because we have a handful of developers stating that they aren't working on anything NX or don't know anything about NX doesn't mean none of them will be making NX software, even for the launch period. The fact that we already have these 7 rumored games I listed should actually be encouraging if you take every rumor at face value, because I don't remember this many rumored games from when the Wii U was launching.
It's just best to keep in mind that this industry is VERY secretive, Nintendo leading the charge in that area, so the lack of evidence of third party games does not indicate that there won't be any.
Edit:
Nothing is leaking because of the NDA. It's the world's first completely effective NDA. Sony and MS should look into however these NDAs are written. Of course, if they could even find the NDA. This NDA is so rock solid it's hard to prove it exists. But we know it's there. It's like the illuminati. It's the IllumaNDAti.
Actually I would wager that Sony and MS know the value of a few leaks here and there to drum up hype. Nintendo on the other hand sadly believes that any sort of leak is a failure for them, even though often times leaks can be good things.
People really think this thing is going to have 3rd party support too.
The Wii U launched with a relatively impressive number of third party games. Not the best quality since many of them were late ports, but the games were there nonetheless. I don't expect any less at the NX launch.