Lots of sources are saying that with star position/velocity information, scientists can rewind or fast-forward time to see how the Milky Way looked hundreds of

Lots of sources are saying that with star position/velocity information, scientists can rewind or fast-forward time to see how the Milky Way looked hundreds of millions of years in the past/future. Does anybody know how they're solving a 1B+ element n-body problem with enough precision to make that kind of claim? I thought these things were so chaotic that this kind of prediction was impossible?