The *degree* of asymptomatic transmission of novel coronavirus was (and, I think, remains) unclear. As to when we knew that it was happening, here& #39;s Dr Fauci on January 31.

Here& #39;s Fauci on that point March 3.

And here& #39;s Birx (Coronavirus task force coordinator) on March 14, addressing the how-much-not-whether question and how policymakers should proceed pending data.