"And it seems to be quite accurate."

I think the right word there is "precise", not "accurate".

In reality, there are so many unknowns down to exactly how much dark matter or energy there is and exactly how it's causing expansion, are we in a single universe alone, a single universe with bubble sub-universes, a true multiverse of 3-branes, how does the quantum foam at the Planck level affect (or even cause) this expansion and so on, that any notion that we "know" with certainty (and thus accuracy) and can predict the progress of the universe as it ages in a little presumptuous.