On April 27th, Nintendo will be giving an update on their financials with their next Fiscal Year Earnings Release. Naturally, Nintendo will also be giving an update on their perfomance for the overall Fiscal Year on March 31st which should shed some light on Switch Sales as well.
April 27th 2016 was when Nintendo announced that the Switch will be releasing in March 2017 and that Zelda: Breath of The Wild would also be launching on Switch as well and that it was the only confirmed game at E3 2016 For Nintendo. Fire Emblem and Animal Crossing Titles for mobile were also announced on this date. That doesn’t mean that Nintendo will do something similar this year but you never know.
Source: Nintendo (Japan)