So... there's a couple of points here to digest. Because this is a very complex issue.
1. I see a lot of people saying 'don't market the game too early'. Most of the time that's unfeasible. For a game to be announced/shown 6 months before release let's say and then get good sales it must be a VERY popular franchise with VERY good standing and a VERY trusted developer (even Nintendo doesn't always have that amount of trust!). Hype cycle is something that regrettably HAS to happen for a considerable amount of time for a game to get traction (there are a lot of projects that have failed sales-wise because they didn't gain the proper marketing traction timeline-wise).
2. When it comes to marketing early, we get to a catch-22 situation. Be absolutely honest and showcase what the game really is (which is, 75% of it would be a broken mess), people will be like, 'what the fuck is this shit'. So, some segments are polished up specifically for those demos, some WIP mechanics are scripted to represent what the developers want those features to become in the end.
3. And here we get to the No Man's Sky situation. The 'lies'. This is actually part of the reason why many developers try to be as secretive as possible and show/announce things that they're SURE are gonna make it. Because if something is announced, and then not put in the final release of the game, that is considered to be a 'lie' now. Which is really not true. 99% of the time developers do not lie, because at the moment they're talking about a certain feature they're working on it and expecting it to be in. And sometimes features have to be literally cut last moment because even though all the important parts seem to be there it just doesn't work, or after scaled up testing you start seeing that everything just falls apart and it's better not to have that feature.
When it comes to No Man's Sky in particular, it's a shame what has happened, but let's remember that it's a project that, at the time, was essentially made by 15 very excited about their game people with little marketing skills. They worked on a lot of cool stuff and they wanted to share about it, because they fully expected that to be in the game. Only it didn't turn out that way in the end. And also there's the fact that NMS didn't really have anyone versed in marketing so they didn't have a 'stopper' that would prevent some of those situations, but that's a different issue.
Some of the most beloved games out there have a bunch of stuff that was faked in their demos (because it wasn't ready) that was used to hype up people and then by the end of the dev cycle the devs managed to implement that feature. This happens much more often than you can imagine. Most of the time it isn't talked about because it's not a fail and just seen 'as expected', and it's the fails that are discussed because that's the situation where the developers didn't manage to meet the targets they were aiming for.
Again, yeah, sometimes there are active bullshit marketing pushes. That happens. But those are the exceptions.
At the end of the day games are a mess of different stages of brokenness until the final months before release, there's really no 'best moment' to show it to the world in a way that's fully, let's call it, 'honest', i.e. showing the game in its actual state. Because showing games in their actual state will lead to many potential buyers thinking that that's what it's gonna be on release, just due to the emotional reaction ('oh this looks like shit', - now 'shit' is associated with that game, even if by release it gets insanely polished), so stuff is prettied up and whatnot.
Even when it comes to publishing deals - you can't really show potential publishers a version of a game that's WIP. You have to either show some CLEARLY not completed thing full of placeholders and stuff, OR a very polished sort of vertical slice demo. Anything inbetween will sour the the impression, and we're talking about pitching to people IN the industry who should know better really, but that's just how human mind works.
This is why this is such a complicated question. You want to market the game early so it would have better chances to make a profit on release, and you want to market it in such a way that shows what it would be on release, but you can't do that without a lot of custom/scripted things because at that moment the game would be mostly broken because that's how games are while in progress.