Under voting and over voting is a real thing, otherwise there wouldn't be a need for recounts, ever. Some states do automatic recounts when the margin for victory is .05% . Some do more, some do less. The .05% example is Minnesota's margin for an automatic recount. Using this figure

People who voted in the 2016 election: 139 million

139mil *.05 = 6.95mil Would ya look at that, 3 million is within the margin that would require a recount in plenty of states and/or districts. But there isn't recourse for a national recount of the popular vote, only for individual states and districts. So there's no way of telling if anyone really won or lost the popular vote because it's too damn close and it doesn't matter anyways because of the electoral college.

(Not to mention the dead people voting, illegal residents voting, and general voter fraud that's been dug up recently.)

So no, 3 million is not a static number.