NPD and Famitsu/Media Create are not 100%, you can't take their numbers and say that's 100% sell through, it is still and estimate. They don't literally count every single system sold.
Switch should do better because it has a real game in Zelda BoTW that can appeal to core players. They weren't dumb in launching with Nintendogs + Cats as the main launch title, if they had, it would be selling worse than the 3DS.
But the first 2 million of any system sells fairly quick, even the Wii U cleared 2 million in sell through in about a month. If you restricted Wii U stock to only 2 million total, Nintendo could claim the same thing with Wii U (a complete sell out with shortages). 2 million is fairly easy to sell these days especially if you aren't competely incompetent.
When they have shipped 4 million and are still experiencing complete sell out and you can't find the system anywhere, then that is a different story.
