I'm not a big fan of "hard" dates in Star Trek. When the idea of the Eugenics wars was first presented in TOS it was meant to be something that was in the not to distant future. As Star Trek progressed, some of those dates don't really hold up anymore. The Eugenics wars and Khan and his people leaving Earth in his sleeper ship are a perfect example of this.
I know that in later projects like Voyager, they still referenced those events as taking place in the 90's, but I prefer to look at them the way they were presented in TOS, in the not so distant future. So to me, the Eugenics wars still haven't happened yet. After all, I think we would have noticed them. I just kind of gloss over the lines of dialogue that placed those events in the 90's. With the level of knowledge that we now have in genetic engineering, it's not to hard to picture Khan and his ilk being right around the corner.
My way of looking at it isn't for everyone, some like to try and fit it into the real world history.