By Dec 31st 2017, Nintendo Switch was 14.86m shipped and ~13m sold-through.
It will probably be at 18m shipped and ~16m sold-through by March 31st 2018.
So, By Dec 31st 2018 I would say Switch will be around 37.86m shipped and ~36m sold-through.
And by March 31st 2019, 42m shipped and ~40m sold-through.
>>>So, for just Jan 1 2018 to Dec 31st 2018, my prediction is 23 million sold-through