Ancestry bases it's findings from other samples that it has received. When I had the test, the results were collated from 3000 reference samples. The database has recently been updated and my results are now collated from 16,000 reference samples. Hence, the results have changed. What I would like to know is how long ago the DNA is sampled from. I guess that DNA threads die out over time and only those from the last few hundred years show in the test with any significance.