I think they already know they're not hitting 20 mill. That was likely largely a target based around Labo become a hit sales driver that would've built through the summer and blown up as a must have holiday gift for kids with tons of social media buzz, but it's nowhere close to that.
But there's no point in revising down now. They'll wait until Q3 (Christmas quarter) is over and revise the forecast down in January to something more realistic.
Anything above 17.5 mill is not bad, the PS4 did 17.7 its second full fiscal year so you can't exactly be mad with say "only 18.3" or something.
If they are certain know they dont hitting it, they would lowered forecast few days ago.
Even if they dont hit 20m, they will be close to I dont think they will sell less than 18m (9-10m in Q3 and 3-4m in Q4).
They're under no obligation to say anything.
Nintendo has revised forecasts down and almost always they do it after Q3 because why give yourself unneccssarily bad press before a holiday season for no reason? There's still a chance (probably a slim one) that they can hit that target anyway.
No reason to revise now, it's better to do it quietly in January when you share Q3 results. A sales target is just that, an estimate, it's not an iron clad guarantee or something a company is bound to. Even if they don't hit their hardware target they likely are gonna beat their software target, so they'll probably have that to point out too.
Because Labo has likely performed no where close to a system seller they likely know internally that it's going to be difficult to hit that hardware number now, the plan likely always was that Labo would be a fairly healthy sales driver in conjunction with Pokemon Lets Go and Smash, not just leaving it all on PLG and Smash. The third part of their equation hasn't worked out.