Why do people assume ancestry results from these DNA tests are "accurate"? Human ethnicity is a continuum, not distinct pools of genes. We are applying labels conceived by modern nationalism to several thousands of years of migration and intermarriage. It would be great if people stopped treating ancestry results from these tests as authoritative reference.
There was a controversy about Korean & Japanese ancestry results from 23andMe where ethnic Koreans are sometimes classified as >30% Japanese. These two groups shared common ancestors since ancient humans migrated via the Korean Peninsula to the Japanese archipelago centuries before the modern nations of Korea and Japan came into existence. Slapping either one of these specific labels on shared ancestry is wildly inaccurate and short sighted.