this is a well known fact now, the decline in january from december, is huge just look at every console sales for the past 5 years, January has been a slow month for years now. DEcember is huge because of Xmas people wanting to buy gifts for the 25th. you do know no we have official numbers, from nintendo, media create and NPD, so vgchartz job is very easy, it's very basic estimates
And that's exactly why Nintendo wanted to ship everything they had for holiday season and December and pritorites that over January shipments. Sales can be good for January sales or despite its January, you cant say they are nothing Switch sales after 24. (December assuming) are nothing special because you don't know that, we only have Japanese sales with huge stock problems but despite that Switch will finish month with around 250-300k in Japan.