So you link me an article that mentions 6 players, all of whom stayed past the 9 game deadline? It's almost like most teams don't consider the 9 game deadline a real thing and that it's the media who hypes it up.
EDIT: Whoops, Yamamoto went back - I was confusing this season with last season.
Yes they stayed past the 9, but they stayed the whole season, and that is the point. And yes Yamamoto went down exactly at 9. The point of the link was to show that team are considering the 9 games.
Now If you look at that draft class the next season, when these guys are in their +2 year and are more likely to get a couple game look, you see that if a player has CHL eligibility, then that player either plays less then 9 and goes back, or you stay in the NHL for the entire season.
I think there was one exception, out of 7 or 8 guys. Now if you have AHL eligibility you see teams more willing to cross that 9 games. Yamamato again being an example of this. Though Necas was a guy who went back to the AHL after 7 games, and Rantanan a few years back played his 9 games exactly and was then sent to the minors. But in that 2017 draft you see a handful of guys who cross the 9 games and then get sent down to the AHL.
Is it a hard fast rule? No, but judging by their actions it certainly looks like a line that teams consider pretty strongly.