I'm inclined to think that Future Ted isn't remembering most of the events correctly, nor is he accurately describing the amount of time they spent at MacLarens. When it comes down to it, I doubt his tale of Barney's sexual history, for one thing, or general awesomeness is anywhere near accurate.
This week's episode is a perfect example, as we see the exact same event (even with the exact same dialogue) play out in three different ways from three different points of view.
On top of that, we see Barney attempt to insert himself into the story, when he wasn't even there. Chances are that has happened more than once in the past, and Barney's history is being exaggerated. We already know that Barney takes credit for things that don't exactly happen the way they appear.