Define "blacked out". Drinking to the point of passing out? Or not being able to remember things the next day?
In the case of the latter, I've seen people perfectly coherent - drunk, but coherent - who remember little of what happened the next day. I've seen people who leave a bar at 2AM, go out to breakfast at an all-night diner and get home with a smile on their faces at 4AM, and remember nothing past midnight. Their memories can be jogged if you tell them bits and pieces of what happened, and often it gradually comes back to them over the course of a few days.
And I've seen people drink to passing out - right on the bar, or to where they had to be carried to a tax or to bed - who remember ever moment of the evening.
The mind is a funny thing.