SuperNova on 23 February 2017
Gamestop released a statement saying 500000 Switches had been preordered through them and they had a 250000 waiting list.
They have also recently recieved a surprise shipment and opened pre-orders again. This might indicate Nintendo shipping more than the intended 2m for launch, as the next shipment was originally supposed to be in april.
This is one retailer in the US and as far as I'm aware the only official numbers we have.
